I can see trying to get enough to remain fully compatible, or maybe as the ebb and flow of upgrades go. For example, I have an A4000D, but as far as upgrades go, it seems the A1200 gets most of them. But I could still kind of wanting an A500 along with it, for those few programs that just refuse to run on an AGA machine.
For example, I currently have a 1040STf, MegaSTe, TT030 and Falcon030. Each one of those are compatible/capable in their own way. Unfortunately only the first and last actually boot to a desktop and the first one has weird vertical lines worth of pixels missing

Still working on cleaning up whatever mice left in the MegaSTe, and for some odd reason the TT030 just gives me a white screen.
But that's part of the fun, tweaking and fixing the old beasts!
Not sure if you'd consider me a hoarder of Atari things. Mostly I think it's a somewhat good idea to have a parts machine as well, but the people who just have garages full of things that sit unused....