Hearthpwn

Savagery
I am hesitant to fiddle with this card. Right now it is horrible value - but if something like Worshiper ever becomes a general use card instead of being AI unique, the card will adjust itself. Of course, we can't count on that happening. If I were to adjust it within the current play environment, I would switch it from one target minion to two random enemy minions.

Naturalize
This is a card in search of a deck. In spite of all the bellyaching, it is still the single cheapest removal card in the game. Unfortunately, there aren't many cards worth removing in this manner until the late game, when your opponent will have enough mana to play whatever cards you give them. It may be slightly better now that Deathlord exists. If I were to adjust it, I'd split the difference between this card and Assasinate, making it cost 3-mana but only giving your opponent 1 card.

Soul of the Forest
Soul of the Forest really isn't that horrible. Like all AoE effects, it was priced on the assumption that it will have 4 targets. The only real problem is that Savage Roar is both a better and a cheaper play under the same circumstances. If the summoned Treants had either Charge or Taunt, I think people's opinion of the card would change greatly.

Healing Touch
The real issue here is that Blizzard has a formula that makes larger healing effects less mana efficient than smaller healing effects. If Healing Touch had the same cost per point of healing as say the Earthen Ring Farseer, it would cost somewhere between 1 and 2 mana and would generally be generally viewed as having outstanding value.

Bestial Wrath
This card is basically built for a Hunter Zoo deck. The only real problem is that agro hunters tend to go faceroll rather than board control. If you don't care about board control, Bestial Wrath does nothing for you. So how would you change this? More cheap beasts with 2 or 3 health.

Kirin Tor Mage
This minion was always solid. However, the odds of converting on the ability (or at least of getting any real value by converting on the ability) have always been slim. However, every new Mage secret makes this minion stronger, so it probably doesn't need to be adjusted.

Ethereal Arcanist
All things considered, playing a mage secret represented a not-insignificant tempo loss making it difficult to get the full value from this minion. Once Mad Scientist becomes available, I think that will change. Instead of 2-cards that could negate the tempo-loss, the mage will have 4 cards capable of negating the tempo loss. Nothing needs to be done to this minion at this time.

Blessed Champion
Blizzard clearly thought this was going to be the Paladin's answer to Bloodlust, that's the only reason I can think of to justify the high cost. Just one problem - it has nowhere near the damage potential of Bloodlust. If you use Blizzard's assumption that AoE = 4 targets, Bloodlust represents a (conditional) 12 damage burst. There is exactly 1 minion with 12 attack, and since he is Deathwing, combos are out of the question. Of course, Blessed Champion is also a persistent effect which normally justifies doubling the cost or halving the effect when - so that means Blizzard expects this spell to be cast on a 6-attack minion, in which case I think they're using the wrong pricing model.  Permanent stat bonuses usually cost 1 mana for 2 stat points - so I would adjust the cost down to 3 - or maybe 4 (to cut down on Leeroy & Blessing of Might abuse).

Holy Wrath
I agree with the OP. It's bad enough not knowing how much damage you're getting for your 5 (well, okay 4... you still get to keep the card) mana - but to also run the risk of overkill or underkill makes it hard to ever get any real use out of Holy Wrath. If necessary, instate a 10 damage cap.

Eye for an Eye
Again I agree with the OP. Either that or scale the damage upward.  Maybe it does 2x the damage received to the enemy hero. 2 damage for 1 mana is still okay value.

Redemption
I think this card is going to balance itself back out, especially with all the new Deathrattle effects.

Repentance
I agree with the OP. A secret can have minimal effect, but it should never have no-effect. Repentance should only proc against minions with 2+ health.

Humility
It isn't just that Aldor Peacekeeper has the same ability - it's that the Peacekeeper is actually more mana efficient about it. When you play Humility, the effect costs you 1 mana. When you play the minion it only costs 1/2 mana. Rather than changing the effect, I'd reduce the cost of this card to 0.

Light's Justice
This card isn't actually all that bad - it just requires one of two things. 1) A reliable way to reduce a minion's health to 1 (like making the proposed modification to Repentance) OR 2) Some way to buff the attack before T5 (when Spiteful Smith and Captain Greenskin become available)

I'll be honest, I don't play priest all that often - so my thoughts here should probably be taken with a grain of salt:

Prophet Velen
The weird thing about Velen is that he is basically designed to be a 2-turn kill. One turn you play him, and the next turn you do 30 damage with Mind Blast and Holy Fire. It puts him in a bit of an odd position as far as Blizzard is concerned. Making him cheaper just increases his utility for 1 or 2-turn burst kills. Making him stickier does the same... and so does introducing more damage spells. In other words, any normal measure to improve Velen flies directly in the face of Blizzards "no OTK" philosophy.

So here's what I would do. Instead of having Velen double damage & healing - I would have him reduce the cost of damage spells, healing spells, and the hero power by 2. Now he is guaranteed to have same-turn utility, but because of the limited arsenal of damaging spells available to Priests, he is far less likely to produce burst kills.

Mindgames
The card is neat, the card is fun, and the card should also be a cantrip. This would also bring the card more in line with Deathlord - which gives your opponent a free random minion without shrinking their hand size.

Shadowform
First off, Double Shadowform only does 3 damage, not 5. But honestly, that's just a quibble. One instance of this spell is still enough to turn the Priest into a Superhunter. The challenge is building a deck that can take the tempo loss if you get the card early, but can hold its own if you don't get the card until later. I think we stand a very real chance of seeing this card gain popularity this week when people start trying out variations on the Naxx rush-Priest.

Holy Fire
I have no problem with this card. That said, I would still be happy if there was something analogous to spellpower for healing effects. (Who knows, make it a neutral card and it might even fix Healing Touch at the same time).

Lightwell
I agree with the OP 

Mass Dispel
Here I disagree with the OP. Naxx has not (yet) made Mass Dispell particularly good. Most of the deathrattle effects that have been released are so wee that they're not worth spending a card to deal with. Then again, that might change this week when the Undertaker gets more people trying out all deathrattle decks. Either way, I think the card is currently overpriced. Blizzard used their usual formula of cost for 1 target (1 mana) x 4 targets (AoE) assumption, forgetting that you are almost never going to face a board full of enchanted and card-text minions.  I would probably drop the cost to 3.

Silence
Silence basically suffers from the same problem as Naturalize. By the time you start facing minions that you actually want to use it against, you will no longer need the extreme mana efficiency that it represents. I would get around this by allowing it to target any played card - including weapons or secrets. Congratulations, your Sword of Justice is now just an overpriced Light's Justice. Have fun with that.

There is, of course, the option of using Silence on a friendly minion (like an Ancient Watcher) - but I honestly think Wailing Soul is going to become the more popular card for plays like that. Of course, there is one place where Silence gets great value and Wailing Soul does not... if you run the Venture Co. Mercenary.

Temple Enforcer
The main problem with the Temple Enforcer is that he seems to be designed to feed the Inner Fire gimmick - thing is, by T6 you've either won by the gimmick, or are facing minons so beefy that they can probably take out whatever you buff. Even so, there's always a chance that something will happen to make the gimmick a late-game strategy. I would probably leave him alone for now, though I think the OP's proposal would also work.

Kidnapper
I'm on board with the "put the card in your hand" approach. That said, I like the OPs idea of increasing the cost of the minion after it has been returned to your opponent's hand. However, as much as I like the +2 mana cost idea it does effectively turn the effect into a kill against most late-game Legendaries, so I think it would need to cap out at +1 (where it only "kills" Deathwing).

Patient Assassin
This card is tied with Naturalize for being the cheapest universal kill effect in the game. Unlike Naturalize, it doesn't give away cards which means it needs to be vulnerable. 1/1 is fine - a 1/3 would need to cost at least 2 mana.

Vanish

The problem with this card is that it usually gives tempo to your opponent. However, it works well in weapon centered decks and is still one of the best options for mill/card burn - so I probably wouldn't mess with it.

Sinister Strike
Spellsword Rogue isn't as popular as Miracle, but it's still a viable deck type.  I would not mess with this card.

Totemic Might
Ah yes, the combo card that exists for the sole purpose of ensuring that your totems can survive until Bloodlust. I have a feeling that this card will get stronger because Blizzard will eventually introduce more Totems. If I were to rebuild it for the current environment, I would increase the cost to 2 or 3 and change the effect so that it doubles the stats and effects of every totem in play.

Frost Shock
Definitely weaker than Earth Shock right now - but I bet it will be very popular next week to deal with a certain skeletal dragon. Within PvP I think it's going to depend a lot on which direction the meta goes. While everyone runs around with text-effect minions, Earth Shock is better. Should it the meta switch to vanilla minions, Frost Shock will start gaining popularity. For just this reason, I think it can be left as is - it's insurance against future changes in meta.

Dust Devil

Dust Devil is a gamble, pure and simple. If he lives, you're in great shape. If he dies you've just taken a significant tempo loss. The main problem is that he is not sticky at all. To make this card viable the Shaman would need some way to give him health (or divine shield) for little to no mana. Changing him to a 2/2 would make a huge difference, but it might also make the little guy too strong.

Far Sight
This card seems more like a deck-building challenge than anything else. My guess is that you'd want it in something that looked like a cross between Miracle Rogue and Ramp Druid (cheap spells, expensive minions, and a couple of Gadgetzans). That said, this thread is about tweaks. If I wanted to tweak this card to make it more reliable, I'd turn it into Tracking with a 1 mana discount on the selected card.

Battle Rage

The "problem" with Battle Rage isn't with the card itself, but rather with how we tend to look at it. It costs 2 mana and seems to have a huge amount of synergy potential, so it is typically viewed as an under-performing Starving Buzzard/Unleash the Hounds combo - but it's not. It's an over-performing Arcane Intellect.

Incidentally, if you are having a hard time pulling off Battle Rage combos, you might want to consider running Commanding Shout as well as Whirlwind.

Charge
There is honestly nothing wrong with this card - it simply fills a different niche from the Warsong Commander. If you want to run Yetis, Ogres, and Harpies - Charge is better. If you favor Worgens, Berserkers, and Pirates then the Commander is better. The Warsong Commander requires you to tailor your deck to fit it. Charge is finishing support that can go into any deck.