Also a card that can turn any enemies territory's to a neutral and add %250 the armies
It's too much OP as a card, you can just use it on a very large bonus he controls and then he gets a serious income hit, or you could just use it on your ennemy stack as well and get rid of the problem. It's rather bad to be used in strategic games, maybe it has it's use in diplos, but not for strategic games.
For the card "market" (I'll use the name that some1 with a close idea to yours used), it'd be a thing that would be very interesting to have.
Edited 3/24/2016 17:52:00