Back when I could still find them in that price range, I also found that they would frequently get flaky or crap out all together after a while. It's also all too frequent that I put a machine away in perfect working condition, only to pull it out of the closet months/years later and discover that the hard drive has died. For me it's not a matter of profit, nor am I especially cheap, but I just can't bring myself to spend $130 on each of half a dozen vintage machines to replace the temperamental ancient hard drives with dependable, silent solid state disks. $50 is about the magic price point where I'd just buy something that would do what I want. Otherwise I'm more interested in a DIY solution. I just know what while the hardware I can do, it will die on the vine if I'm developing the firmware myself.
Another motivation is just the cool factor of seeing what interesting hacks people can come up with. I mean honestly why else do we play with these ancient computers but to have fun with them? It's not like they can actually *do* anything that can't be done by a modern $200 netbook.