Ask HN: What's the best way to clean out a music library? (iTunes)

This is a tricky one, because it's hard to know whether someone will want to listen to something in the future or not. Based on whether or not as song has ever been listened to ... has a decent rating ... and/or is part of an album with a significant number of other tracks meeting that criteria, what's the best way to clean out unnecessary MP3s on a large scale? Typically with something like iTunes, and aside from moving to a streaming service like Spotify or Rdio.