Retro gaming is big, will probably beomes bigger too. While I have retro gaming machines, none of them are 486 based (tandy 1000, 386/40 and p200mmx for DOS), I use my (3) 486 for messing with OS and doing Windows 3.1 programming (when I get around to it). I also collect VLB and EISA cards and need machines to put my ISA capture cards into.
Anyway yes, I have seen complete system "setup" for DOS gaming go for $100+ sometimes, but that is because they are hard to find these days outside of ebay and the landfill. I don't know anybody who has a saved 486 anymore, p2's are throwaway and more usefull so why would you keep a 486?
Its not just any 486 box either, you tend to see them with both 1.44 and 1.2MB drives, a decent soundcard, and a VLB video card, plus a cdrom and a few shareware games loaded. From the buyers point of view coming up with all the parts configuring them (jumpers suck), and getting them shipped is more of a pain and costs more then just buying the box all setup and ready to go.