Bah, I like this game cos it's balanced.
Atm rare cards simply bring new combos, and make a little stronger the existing combos.
Any OMGWTFBBQ ultra-rare card will just ruin the balance and will make the game unplayable.

If you want to create addiction to this game just make a new model for the existing rare cards and make em pay 20k each. This way the "addicted pros" will have their ego satisfied.