I think if you want a Wii you've probably bought one. And if you haven't been convinced I haven't seen anything that would change your mind. Early on in a console's life so much is based on potential so one big game can win you over. You guess what the future will hold and gamble based on that. But right now we know where the Wii is and where it's going to be in the near future. I personally think that the Wii is in an N64-like rut where some amazing first party game is released and then we wait and wait until another killer first party game is released and there's not much in between. And I don't think that's going to change. The Wii is number one. If that doesn't convince the third parties to make their big games for it, nothing is. Unfortunately, and somewhat illogically, this is the Wii's mold.
Meanwhile the PS3 only recently became affordable so there are going to be people that wanted one but couldn't afford it and now they can. And in Japan there's no Xbox 360 dominance. The PS3 is the go-to alternative to a Wii. The PS3 is hot right now in that it has big games, both first and third party, coming out on a regular basis. You can point out how there aren't many exclusives as most of the third party games are also on the Xbox 360. Yeah, but again this is Japan. No one buys X360s there. Any big PS3 game might as well be an exclusive in the Japanese gamer's mind.
The PS3 has potential while the Wii's mold is very set. If the Wii didn't interest you enough to buy it then, it does nothing to change your mind now and I don't think anyone thinks things are going to change.
Plus if Super Mario Galaxy 1 didn't convince you to take the plunge why would the vastly similar Super Mario Galaxy 2?