For those of you with a collection of music from the iTunes Music Store, perhaps you feel you don't get your money's worth by not listening to your purchased music enough. For you I offer this:
To Get Your Money's Worth:
Type is Protected AAC audio file
Last played is not in the last 3 days
(or whatever frequency you want it to be)
Optional addition:
Play count is less than x
(if you only want to cycle this music for so long)
or
Date added is within the last 1 month
(again, however long you may want to cycle the music)