Wii Sports Resort has sold half a million in Japan in two weeks.. The sports minigame compilation genre may be packed but there isn't one that is the sequel to the best selling video game of all time. There is also no other title that shows off Wii MotionPlus as well or one that has the depth of Wii Sports Resort while having 12 different sports.
You also forget that Nintendo will be pushing this game HARD with the biggest advertising campaign they've ever put together.
Aside from that, yes I beleive Wii Fit Plus is being released to combat the other fitness titles coming soon or just released that do certain things (designing a workout etc) better. Just as Microsoft and Sony move into the motion control space, Nintendo will try to take the focus off of 'motion control' and onto 'superior software.'
The Vitality Sensor will expand the market, yes.. But it will also be a device tries to show consumers that it isn't all about motion controls, it's the games that use them that are fun, just as the balance board would have never been successful without Wii Fit or the Wii Remote without Wii Sports. The Vitality Sensor will only take off if the software is strong and Nintendo will want to show that.
