It seems to me like Tokyo Disney will be popular whatever they do, just by virtue of it being the biggest park in Japan, and the Japanese being obsessed with Disney. I could be wrong, but I get the feeling they've not done any major re-modesl/expansions there for a while, so is due something on this scale. Why spend money re-imagineering something new when they can copy and paste this. They need something new, it doesn't really matter what they get, and they've got this ready to go, so why not? As others have said, there's barely anyone who will have been to both California and Tokyo so they need to worry about that even less than for Florida. I'm not particularly comfortable with the idea of copying it, but from Disney's point of view, I can't see any reason not to.
Oh, and, I don't have time to find more up to date figures, but in 2008 Tokyo Disneyland had 3rd most visitors. Disney's California Adventure was 13th with almost 1/3 as many visitors. So, yeah, which one do you think needs to worry more about "bringing people in"?