I would think that Spendthrift would be a variation of Charitable (-15). The effects are similar, in that you're always throwing away money that should be kept for more important things. Charitable means you really just give your money away on a regular basis (but you may make friends in doing so) whereas spendthrift has you regularly buying silly things which you get to keep (though creditors chase you and bars refuse to give you a tab). I would think they're comparable.

I had a character that was built partly around the charitable disad. He was a carnival performer who would always blow his money buying rounds for everyone else after each show, never realizing that that was why he was always broke.