What's the point of talking crap about Wii Sports? It is free, it is a good game. Because of that it's value is high. As for replayability, does it matter (free remember)? I don't think buying a Wii for Wii Sports is a good idea.
Yes... buy a Wii solely for the purpose of playing Wii Sports.
Wii Sports isn't a gimmick, people are fickle consumers.