I think you might get more support for these kinds of ideas with a little more liberal pricing structure. With smaller units being offered.
The donation math is a little flawed. People donate to reward the dev, and continue game development. I think you can't assume that people are always donating for cards.
Entry level offering is $25. That's too much.
I have no doubt that you could sell your Nymphs to a segment of the players at 17 cents each, but a 144 minimum bundle limits your takers.
$25 buys a number of full games on your average Steam sale.
Keep in mind that every single Elements player falls into the category of "Plays free games."
Keep also in mind that once you start selling advantages, it creates a rift between players. Resentment leads to player loss. You see it in all the "free to play, pay for advantage" web games out there.
Don't get me wrong, I am 100% behind the developer being able to make a living, and I support any number of indie game developers (168 Steam games alone), this idea needs some tweaking though.