I could only see myself buying it if a really good game comes out that supports it. Otherwise, there's no need for it, as I don't by shovel-ware anyway.
Fair enough, Super Mario Galaxy is obviously more kid-friendly than, say, BioShock or Call of Duty 4. However, it's significantly longer than both of these games.
Super Mario Galaxy: second highest rated game of all time and winner of both IGN's and GameSpot's game of the year awards. I'd say that's a "must-play" game.
By the way, the same argument can be used, perhaps more justifiably, for any other system. If you're going to explain why you don't want a Wii, a better argument would be, perhaps, that it is much less powerful than other current gen systems or that it doesn't have very many good games.
