If you regularly have two or more people at your house who are unskilled gamers, including many young women, older men and women, or children, a Wii is great for you.
I'm not dogging on the system at all, but there are very few "serious" games for the Wii. My father owns one and owns (amazingly) the majority of the games available for the system. They're all collections of mini-games, platformers, or novel uses of the Wii-mote and nunchuck. As you noted, there are very few deep and/or expansive games, especially if you're a PC/Xbox360 gamer.
Metroid Prime 3 aside, there is nothing comparable to GoW, CoD4, Halo3, Oblivion, Battlefield2 or Bioshock on the Wii.
If you're a mobile gamer (and it sounds like you might be, as a PSP and GBA fan), then the DS would be pretty good for you. There's some very amusing games, and despite the ridiculous amount of Zelda clones, the new Zelda for DS is quite fun - stylus boomerang throwing FTW.
I'd look at trading in the PSP and some cash for a DS, and then spending the rest of your Christmas money on bills. They'll haunt you forever, otherwise.
