With few exceptions I generally stay away from buying the same game more than once as long as my original copy still works (Enhanced remakes don't count). My virtual console library doesn't have any repeats of games I already own but I think the one game I would repurchase is Donkey Kong 64.
I'm a relatively new HDTV owner (had it for a few months) and certain older games don't hold up very well visually. Sadly, DK64 is one of them. Since the Wii outputs at 480p, there'd be a pretty noticable difference as far as sharpness and jaggies are concerned, not to mention the slight controller delay would be eliminated. I really enjoyed DK64 back when it was new but I just can't see myself replaying the game from start to finish again unless its on the VC. As of right now, that's the only game I think I'd double dip on.
How about you?