It seems like an entertaining thing to do for a short period of time would be to listen to a few songs with very different equalizer settings. Every time I listen to a song on new speakers or headphones I seem to hear something different. Just now I noticed interesting little background effects on Inama Nushif (Bryan Tyler, Children of Dune) that I didn't realize were there. When I listened to Good Luck (Basement Jaxx, Kish Kash) for the first time with my new speakers and sub I discovered the explosion of bass during the introduction. Perhaps using equalizer settings would at least simulate some of this, allowing you to focus on ranges of the song that you ignored previously. Of course, the characteristics of a particular speaker are more complex than ten little sliders in Winamp, but it seems like it might still be an interesting exercise.
Right now I'm listening to my playlist of what I decided were my 100 favorite songs as of about a year ago. (Yesterday I played my top 25, and I got to remember why I liked each one so much.) This morning on the way to work I made it to Tristram from the Diablo and Diablo II soundtracks... not only memorable, but really good. I should update my lists soon; I've found a lot of great stuff over the past year.