We have Wii Music and Lego Rock Band for Wii in our house now. They are both good ways of lowering the entry barrier to music. What do I mean by that?
I've seen an attitude with music that what you're doing is not music until you reach a certain standard, you do it in a certain way, on a certain set of instruments. It's a bit like that apparatus you see in some playgrounds where the first step on the ladder up the slide is quite high, to prevent little children climbing up the big scary slide.
With Wii music, you can never play a wrong note. Whenever you make the appropriate gesture or hit the button to get the music out of the imaginary instrument you're playing you get the right note. If you don't do it in time to the original melody, you get a counter-melody. With the super-easy level on Lego Rock Band you just have to hit any drum at the right time to get the points, or just push the "plectrum" button on the guitar, or make any sort of noise into the microphone. With the guitar sometimes you get notes even if you don't get the timing right.
The game designers have made the barrier to that slide as low as they can. Whilst you can't get that far with either game, maybe it will encourage some to try non-Wii instruments - I'm not going to call them "real".