I've gone through this process a couple of times, what with moving from one computer to another, and from one music player to another. Every now and then I'll find some MP3s that I ripped in the pre-Mac days, from CDs that are now packed away and forgotten.
I use a couple of techniques to go back and savour old music that otherwise might fall out of use, even within my current iTunes library.
A smart playlist named "Forgotten Favourites" holds the 4- and 5-star songs that have the oldest "last played" dates. Depending on the size of your library, you could set this up in different ways. It could be all your 4- and 5-star songs, with "limit of N items selected by least recently played". Or it could be all your 4- and 5-star songs with a last-played date farther back than some cutoff, such as "last played is not in the last 12 months", then perhaps with a limit and the songs selected randomly.
No matter how you arrange it, you'll hear some songs that you like, that you haven't heard in a while. And after you hear a song, it will drop off the playlist and be replaced by another.
When I get a new album, I put it on a playlist "Album Appreciation" that I listen to when I have a few free seconds to rate each song. But after a while, it can seem unfair to devote time to new music where there might only be a couple of 3-star songs per album, when there's all this great older music that I'm missing. So every now and then, I'll erase all the ratings from one of my classic albums, put all the songs in the "Album Appreciation" playlist, and go through it again just to remember how the songs work together in order. (Sometimes listening like this, I'll give certain songs a higher rating than if they just came up by themselves on shuffle play.)
PS: Although I refer to "Album Appreciation" as a single playlist, actually it's 2. "Album Appreciation - Raw" is a regular playlist where I can drop a whole album. "Album Appreciation" is a smart playlist that picks songs from the first playlist, but only the songs with no star rating. That way, as I rate the songs, they fall off the playlist that I actually listen to. And when I've rated several albums this way, I'll go back and take them out of the "Raw" playlist.