I have actually found it helpful in the past. Actually, rather than wii I have found this through an old (and cheap, used) xbox and DDR. For me it was a fun way to move around that I could do in the safety of my home, even when I couldn't go out the doors. Since I began playing, I have also been going to the gym on a regular basis (trying for twice a week) - and that has helped even more =)
So yes, I think these games are wonderful! There are varying levels of play and some of them can get you even sweating, even if you're in decent shape (in the case of some friends I used to know).
Thanks for sharing this
Also in answer to your question to play wii you need:
A tv that you can plug the wii into
A wii
The game
Possibly some extra controllers (I'm not 100pct sure on that, but especially if you want to play with other people you may need to go to some extra expense)
In the US, using amazon I see that new wii's are still pricy, but there may be a possibility of getting a used system, or a better price in stores??? It looks to be north of 200 dollars.
Each game varies in price: one of them on amazon looks to be 20 dollars, with a possibility of needing some kind of extra remote (I haven't tried it so I don't want to give you wrong info)
There are other games that use body motions, specifically DDR but these are of a different type, and are harder on the body/ require different sorts of skills that might be hard to pick up at first. You may be able to get some old versions of such games for cheaper though, because they've been out for years whereas the wii is still pretty new.