I think should be a good idea, to support this fantastic free game.
I suggest a skill bonus from +1 to +10 related to % costume unlocked (cant go over the cap of 100).
So a new player can enjoy the bonus and an old supporter can be gifted with a small bonus too.
No pay to win becouse the cap stay always at 100.
No thank you, there would have to be heavy restrictions on it; or you will have this lvl 10 nub with lvl 80 skills and just no the abuse that would get *shudders*