My actual (non-classical) library is ~39,000 tracks, mostly full albums, all of which I've heard at some point during the 20 years I've been collecting them. My "listening library" is a static playlist of the songs I like and want to hear from my library - right now that's at about ~17,000 tracks. From there, like psychoadept, I have a few auto-playlists set up. Mine are based on date added and date last played.
Basically songs can be in the rotation for unlimited plays for the first 6 months after they're added. After 6 months, they're not played within 6 months of their most recent play unless they're tagged Evergreen=Yes. Evergreen songs can always come up in rotation even if I heard them yesterday. They're a handful of favorites.
So I have my static playlist "listening library" and the main "rotation" auto-playlist from that, and then from that rotation playlist comes several auto-playlists for specific situations. One to synch to my phone that is limited to the size of my SD card. One that strips out everything marked as "explicit" which is for listening in the house when my kid is around. One that is only tracks that haven't been heard since their initial 6 month "trial" for when I want some stuff I'm really not all that familiar with but I know I like. The "rotation" playlist and its offshoots are what I actually listen to on a daily basis.
I finally bit the bullet and set up last.fm play data synching so that plays on my phone will remove those songs from rotation when I'm listening at home. That was something I resisted for a long time, but I'm glad I finally took the plunge. I lost a lot of the play count I had been building up since I started tracking that in 2009 (I only started with last.fm in 2017 when I started with MB), but I decided raw play count was more interesting than it was useful for my purposes, while having an accurate all-inclusive last played date would be more useful for my needs.
My goal is to have surprises mixed in with the well-loved and familiar like a personal radio station that only plays songs I already know I like. MB has made that possible.
A smile is happiness you'll find right under your nose.