I'd say it is definitely something worth seeing if you are a music person. Lots of cool stuff in there.
It's been a couple years since I've been there, but there is probably 2-3 hours worth of stuff to see just walking around - but they also play some films that might be worth checking out - and the gift shop is a big time spender also. It could be 4-5 hours if you are really interested and check out everything.
Right down the street is the Great Lakes Science Center, which is also good if you have kids....or just really like science.