The Huffington Post has a provocative article by Mat Gleason about NOT donating to art auctions:
There is a tradition of auctioning original works of art donated by artists to raise money for charitable causes. There are many good causes that hold such events. No matter how good the causes, though, I have come to the conclusion that artists must stop donating to every single one of them.
Don't ever donate your art to a charity auction again. Half a century of charity art auctions have changed the way collectors buy art. These fundraisers have depressed prices of art across the board and kept artists in a subordinate position that has no career upside or benefits