[jonbro]

or even better, have some type of in song currency that is used to purchase the new songs, that can be acquired either through sending the old songs to your friends, playing the old songs well, or just outright buying the in game currency.

I think the new bjork album started going in this direction, but could have done it a bit more.

[minikomi]

Hmm.. gamify it by adding some badges and you might be on to something there!