If you're interested in older games, the Wii is almost certainly worth the extra $100 or so you would pay over the GameCube because it's backwards compatible and, more importantly, will allow you to cheaply acquire lots of classic Nintendo and Sega games; basically, it's like getting a new system + a gamecube + a 'Best Of' collection of the NES, SNES, Sega Genesis and Nintendo 64.
Unfortunately, that DOESN'T include Pokemon, for which you would need to buy a used GameBoy or GameBoy Advance (NOT a DS). :\