I'd like an emporum that lets you offset the cost of a card you buy by trading in cards from your hand. You'd essentially be discarding cards, but with a slight benefit. A fair price would make that huge card stack needlessly powerful. Cards should be most potent when you find a good use for them.
Maybe you could trade in your old cards at a value of 1 (gold) whenever you buy something from them. (Buy card for 8 gold, pay with 3 useless cards and 5 gold,) I would not want a direct conversion between cards and gold, because that would make cards an outright goldmine.
Maybe also not allow more than half the price of a card to be paid in cards. Don't know.
