I have an Asus P2B (full ATX size), a P2B-M (baby AT size), and a very very similar baby AT 440BX board made by "Totem". All three have the same thin green heatsink on the northbridge chip. I suspect it's marginal - probably not technically needed but helpful in a hot-running system. (OC, bad case ventilation, etc.) That sink can't be doing a heck of a lot based on its size, but it still doesn't get particularly hot. Just warm.
IMO, this is when computers started to get stable. The PII (well, 440BX) in particular is also a fantastic bridge between DOS, Win9x, and almost up to 2K/XP. That's probably why they're more sought-after.
IMO, if I found a motherboard I wanted online for $40, I would be thrilled. It seems ~$60 is typical, and it's not a deal-breaker when something I really want starts to get up to $100 or so. Minor repairs (recap) to be expected, but I'll leave the ones with a ton of bent pins and ceramic caps having been scraped / knocked off to someone who is more interested in haggling, and doesn't mind spending more time on resuscitation. I've got one with a couple crushed pins in one of the four RAM sockets. If I had known that, I wouldn't have bought it - despite that I really only need two. (For now.)