There are a lot of good suggestions in the replies here, aren't there?

I was going to say that I've been doing a lot of self-hosting and home automation recently, and it's had me doing things like spending a lot of time finding out if I can run Linux on an old Apple TV, to make it yet another home server running containers. I went through a phase where I was considering disassembling old laptops to re-use their LCD panels as mounted control access points around the house.

However, the LCD thing never went anywhere, because I'm not handy with a soldering iron, but also because I've found that those laptops are usually newer than the ones people in my family tend to have (me being in software and having cycled through laptops frequently), and I've been re-installing friendlier Linuxes on them and giving them away to friends and family.

I wonder about the other devices, though. Many are certainly not low-power-use, and what's the impact of me continuing to use them? Headless, most are certainly capable of running at least one containerized service, but a newer ARM or RISCV board will almost certainly sip less. What's the environmental trade-off?

I have, though, only one tower. I built it in 1993, and have simply upgraded it with new MBs and components over time. It's main feature turned out to be it's usefulness as a RAID5 container, again upgraded with increasingly larger HD over the decades, until the point where I stated prodominantly using docked laptops. One move, I simply never set it up again. That one is a power-hungry monster, and I feel bad about having it powered on 24/7. But I still keep it because, sentiment.

Annecdotes aside, my answer to your question is: most computers can run Linux, and therefore, most computers could find a use in self-hosting. For me it's become more a question if whether I have, or can find, a use for it. Often, a conversation with family results in finding a use; setting up a self-hosted media-server for mom, maybe. If not, it becomes e-waste, and I feel bad for a bit. But my devices have tended to be small form-factor, like Vera or AppleTV; it sounds like yours are larger, and maybe the form factor makes them less desirable to reuse.