A possible clean-ish address for the problem of remembering the value assigned to a wild card: 20 small chits, 4 in each suit’s colour, double sided with each side bearing a revenue value (3/4/5/6/7/8/9/12). When a player buys a wild card they place the matching chit on the card with the appropriate side up so as to record the revenue they assigned to the card.
Unfortunately it means not only an extra component, but an extra component-type. Oh well. I guess I can’t hope for an Adlung-Spiele small-box presentation.