Hearthpwn

I've been tweaking and playing a Reno mage deck lately and have a few questions (sets of questions actually):

1. Why do so many deck guides I see run cards that heal both heroes..Mistress of Mixtures and Refreshment Vendor particularly? Is it because we assume the mage will be taking damage before the other hero, so will make full use of the heal more often? Are we willing to give the other player health early in the game because the win condition is Alex, so it doesn't matter what their health it prior to turn 9, and we just want the bigger body on the board? Why wouldn't it be better to use cards that only heal my hero, like Gadgetzan Socialite or Earthen Ring Farseer?

2. How do I get Doomsayer to benefit me? I've tried using him at turn 2 or 3. I've tried using him in conjunction with a freeze spell. I've tried pulling out another minion with Dirty Rat, freezing them, and dropping Doomsayer. In almost every single case, the other player has an answer to nullify Doomsayer. It seems like the only time he actually clears the board is when the other player decides their board isn't worth saving, smashes my face for 5-10 damage with his minions, and simply lets the clear happen. Should I just be content with forcing the other player to use a significant removal on Doomsayer? Doesn't that small benefit get outweighed by the fact that using Doomsayer at any point means I can't use the revival portion of a Kazakus spell?

3. What about Dirty Rat? Playing him at turn 2 or 3 is obviously a terrible idea. Since I need a way to deal with whatever comes out, that means having a Poly or Fireball ready to take out a huge minion. If Dirty Rat's only utility is to sometimes pull out a minion with a devastating battlecry/combo effect, and it must be held in your hand until at least turn 6 and could be a dead card until then, why not replace him with a card that is consistently valuable? Even if he is combined with MCT, that is yet another RNG that might get you a 1/1 trash minion from your opponent's board and leave him with all the big ones to stomp you down. Is the Dirty Rat "hail mary" really that useful for anything other than the occasional youtube video?