Personally I think Super Mario Galaxy and Twilight Princess are worth owning a Wii for. And of course Brawl when it comes out. But a lot of the third party games on the Wii are pretty bad, especially multiplatform games with horrible graphics(Yes they'd need to tone them down from the PS3/360 versions, but often times they overdo it below the Wii's capabilities) and tacked on motion controls they didn't think about properly before implementing. Its also getting store shelves flooded with crappy budget games that are only being released on the Wii for a quick buck off a larger userbase, much like the PS2 had last generation. But I will always buy Nintendo consoles first and foremost for Nintendo's games, and for me, they do not disappoint. I also own a 360, and play it more(Or, I would, if I actually had it right now, sent it in to MS from the dreaded Red Ring of Death), but I would never ditch my Wii even if I only buy a couple games on it a year, they are usually truly fantastic games to me.
As far as the PS3 goes. I'm hoping to win one through a contest at work for having perfect attendance through the christmas season, and I'd play a couple games on it like Uncharted and Ratchet and Clank, but it doesn't have nearly enough games that are system sellers to me. And I don't particularly care about Metal Gear Solid 4 and Final Fantasy XIII coming eventually, never was a big fan of either series. Its just not worth the $500 to me.
If you really don't like your Wii that much though, you could easily get your money back(And likely more) selling it on Ebay. Might have gotten more prior to Christmas, but its still really hard to find regardless of christmas shopping or not.