Personally I'd rather have a (preferably graphically upgraded) port of GTAIII (compliation) with Godfather like Wii-controls. The great thing with Wii is playing with your buddys. GTA:SA had local co-op play, GTAIV does not.
But if given the choice of merely GTAIV to Wii or not to Wii... I'd say no. Probably be too many compromises, and it'd seem so counter to what Wii is.
I might get a 360 at some point and if I do, I might (more likely my son would) get GTAIV. But I'm not sold on the game at the moment.