Originally the card turnin was going to be a point based system. But point assignment is extremely subjective, coupled with some cards actually drop more commonly it would create a scenario where you could by your top rank cards in a shorter time by turning in the low grade cards.
Its not necessarily a bad idea, but getting the economy value balanced with its game power and its relative difficulty in acquiring is all a problem that and we don't have a lot of spare variables floating around to utilize in such a tracking system.
I can make you a value list, and to avoid radicals when a new update is implemented effected cards can simply be entirely removed. I think race reduction cards could be ignored to just make this easier. Also, MVP cards should not be included.