actually, thinking about it, the 1-card clause makes this competition... weird.
It means cards that make a fg more explosive are probably bad for the deck, as when drawn late it becomes a dead card.
The most useful 1-card additions are most likely a permanent with a passive effect, like eclipse, SoP, or SoFr.
I'd suggest allowing you to choose the number of copies, but no more than 1/15th of the original deck size. (so 2/3/4 at 30/45/60)