There's really not a whole lot left to keep the Wii fresh in minds of many. At this point (four years in) the primary reason to buy a Wii this late is for the current catalog of titles, particularly most titles published by Nintendo.
I really don't see the third party support situation changing in any significant way.
So while there are plenty of reasons to maintain interest in the platform in the back catalog, in addition to upcoming titles from Nintendo like Skyward Sword, existing catalogs generally don't take center stage.
I know, someone will probably chime in about Wii Relax (was this title even announced?!) and the Vitality Sensor, but I can say with a pretty fair amount of confidence that if and when it's finally released, it will not be another Wii Fit/Balance Board.
I agree with the notion that the real future of Nintendo lies with the 3DS. That's where the 3rd party developer support seems to be at along with a lot of enthusiasm from those currently working on titles for the platform.
