1) resisting the urge of hoarding
I'm into Pentium/MMX era, and once I've learnt how to get these parts cheaply or for free, I've been flooded by them. I now have 6 Socket 7 motherboards, a bunch of Pentiums, about 20 Soundblaster and clones, about 30 various videocards, etc. It happens because when people want to give away these parts for free, they usually want to give them in bulk. And it's not like a lot of my parts are unique or I could call it an actual collection.
Don't get me wrong — it's really useful to have a bunch of spare parts and be able to solve any compatibility issue without doing any extra shopping. One time I've even managed to find a spare LED for my case that wouldn't show HDD activity properly. But it does feel like hoarding. I often think about getting rid of extra parts, but then I think "what if something goes bad?"
2) constant rebuilding
Some of you have mentioned that: you always want to go better, faster, etc. With early Pentiums it's not too hard to go really high-end, though, so for me it's different. I'm more concerned with the look and feel of my system: finding a desktop-style AT case, an "authentic sounding" HDD. Right now I'm thinking about a new CRT — my only 17" Samsung 757DFX looks too modern and generic to me and I want something like a curved 14" Samsung 3NE or a 15" Sony Trinitron. For me, a "classic" DOS/early Windows PC should somewhat resemble the proportions of the original IBM 5150 where a smaller screen resides on top of a horizontal case. My computer should look like this, damn it! 🤣

Now, I do play a lot of games on my systems, but it's nothing compared to the time I've spent fiddling with hardware.