Wouldn't it be cool if there was a tiny tiny chance to get a random card every time you play a game, or only if you win.
0.01% chance to acquire a non-golden card after playing/winning in Arena or Constructed.
0.001% chance to acquire a golden card after playing/winning in Arena or Constructed.
Reaching Legend gives you a random golden card, so this can only happen once a season.
The chance of getting a card that you don't already have is extremely low, but chances like this is put in the back of our tiny human brains and because of that, can still motivate us to play. And when you forget all about this, but suddenly it pops up it's a nice little surprise.
Another fix: Make right-clicking a class' tab in the card library open up deck-building for the class you right-clicked.
This is not supposed to be an alternate way of getting cards, it's a nice surprise that create the illusion that every game you play gets you closer to a free card. Games are mostly illusions of accomplishments and luck for things that in the end doesn't matter.
And wtf are you discussing the % chance for a card to be given out, this is brainstorming for a new idea, not a topic for what the % chance should be. I just put it at 0.01 to be subtle. Make it 1% for all I care.