The problem is, there's only so many notes in music, and only so many ways how you can play them differently... and they've all been done before. Everything new is old stuff (melodies, harmonies) which has been played before.
So looking at it like this, you certainly still can produce "new" music. It's just, chances are high that we've heard it before in some other classic songs.
IMO, 70's is even better.
EDIT: 5haz: What about Funk/Soul... you can't just leave that out!