A collegue of mine works at a company that bridged the economic crisis in 2008 by writing a game for the Wii, it is called Aya and the cubes of light.
The game itself is finished, but due to the economic recovery they haven't invested any manpower in doing the necessary quality checks for the publication of the game, so you can't buy it yet.

But I was allowed to play with it, that was the first and only time I ever played with a Wii like game pad!

What I don't know, though, is if there is a low level API for programming for the Wii, the game API is of course rather high level and cannot be used for anything different than game programming. And you need a special license to get the necessary hardware and to be even allowed to program games for the Wii. If there is an appropriate API, I think the cheapest and easiest way to create a little super computer in your living room would be to create a net of game pads.