I finally got tired of it, as well as the multiple switches in the machine room. I got new 8-port switches for the basement and attic, and a new 32-port switch for the machine room. They came in today.
Once I got the switches set up in the attic and basement, everything started running at full 100 megabit speed throughout the house. Whee!
I haven't cabled up the new switch in the machine room; that'll probably happen this evening. I'll retire the old 16-port 10BaseT hub in the machine room; the existing 100BaseT switch in there will become a backup and expansion box. While I was getting ready to do that, though, I did rearrange the center Ivar rack to let me put the serial device server and KVM switch, as well as the new Ethernet switch, in much more convenient locations. There's also room for another serial device server when I come up needing one of those.
Getting all that accomplished was a good feeling...kinda like what I'd been doing professionally for years.