1) Agreed. My solution: "While in your hand: This gains +1 strength when a Zombie is defeated."
2) Power Flower? A legendary? No. Just because it can't be destroyed by very many zombie tricks doesn't mean it should go from a starting card you get 4 of right away to one of the hardest cards to get in the game. Being nerfed to a 3/4 would be fine, maybe it would promote usage of cakesplosion.
3) Repeat Moss...I have mixed opinions about. As of right now, it's just a card I feel should be Uncommon or Rare. But if Popcap/EA nerfs this, then they should nerf some OP zombie stuff, too, like Smelly Zombie (and Deadly in general).