In my late 20's I had a similar thing, but it was due to making so little money that I was just forced to sell basically everything non-essential I owned at the time. My attitude when I had money again really changed my collecting. The stance I have now (for myself, no judgement here to anybody else) is very anti-completionist. I set some arbitrary boundaries on quantity, but one of the main rules is don't get *everything* just because it fits in a set.
My numerical boundaries are largely geared towards the maximum I think I could display nicely in a future where I actually owned a house. Seeing my mom's place and how stuffed it is (no walking room in a 4 bedroom house where one old woman lives) just makes that more imperative. I get stuff, but I cancel about half the pre-orders I make these days after a week or two because I let the FOMO wear off and realize I won't really miss a thing.
I've kinda gotten to like selling stuff. So far, by the time I decide to sell something I haven't yet turned around and regretted it. So I get a little money back and some more space to boot.
Yeah. The "does it spark joy" is a pretty good one. Do I like the look of it? If I dragged it out would I leave it on my desk for a week to mess with it?