In the iTunes Music Store, I've browsed to see if certain albums are being listed (even though I already own the albums) in order to see how good the selection is. In doing this, I've discovered that several albums that I bought in years past have been re-released with additional tracks.
Without iTunes, in order to get these extra tracks I'd have to buy a whole new album. Instead I can just buy the new tracks on their own. So it may be worth your while to check out the iTunes Music Store to see if your favorite albums have been "upgraded." Example: One of the first CDs I bought in the late 80s was Tears For Fears' "Songs from the Big Chair." Back then, it was only eight tracks long. The current version has 15 tracks.
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http://hints.macworld.com/article.php?story=20030803172814955