I haven't read the whole thread, but here's my thinking:
One of the things that really accelerated my disillusionment with Facebook (alongside the toxicity and disinformation) was learning about Dunbar's Number.
Short version of this theory is that most people can only maintain stable social relationships with around 150 people. When you exceed that number, you're actually starting to replace old relationships with new ones.
I think there's a potential corollary to records here. One might surmise that you can only have a relationship with so many albums, but I think that's maybe too limiting. My thought is that I can only have a listening relationship, at least at the album level, with so many artists. So, while I don't have an upper limit of albums that I think belong in my collection, as I get older I find myself less concerned with music discovery and more interested in building out, or continuing, my relationships with artists I enjoy. I won't cap myself at 500 albums, because I know I'm going to buy the next Bill Callahan record, and I won't cap it at 501, because I know I'm going to buy the next Nick Cave record, and so on. But I also know that I'm not likely to just impulse buy a new record by a young band on the strength of a debut single, either, because I don't have the capacity for another listening relationship with a new artist right now.