We use the wii whenever my son is bedridden in the hospital (since all the motions can be done with a flick of a wrist, and uses nearly no effort). If you want to do something that requires more than just wrist flicking, you have to buy several game specific 'mats' to use (like wii Fit, wii Dance, etc.) that are a couple hundred dollars each.
At home, we have a Kinnect, have since it came out, and use it all the time. It's absolutely phenom... but it REQUIRES that you be using your full body (since it uses video of you overlaid in the game) and it can tell very small movements (like whether you have your hand facing the right direction (palm out, palm in) and will correct your positioning (especially for yoga, pilates, personal training... as well as dance games).
The kids use it for HOURS (esp during the 10 months of rainy days we have here), the adults get worn out fairly quickly.
We also use it to stream netflix, do video chat (with friends and family, my son plays a dancing game or build in HaloForge every morning with his cousin who lives across state).
My son just turned 9, and our living room is 8x12, the space we have to use is 5x4