Murphy was out in full force on sysadmin project today. So far the results are
Old Somerville wiring flakieness: 3
Powerline Ethernet: 1
(And that one was a gimme: I deliberately ran my first test within a room — but only later realized I'd accidentally connected both units to extension cords on the same outlet.) I have another approach to troubleshooting it to try tomorrow, but I expect I'm going to end up running about 100 feet of ethernet cable. (I've been trying to avoid that, because the labor involved in doing it right in this house would be immense, and I really didn't want to do a half-assed job. But at this point I just a working wired connection betwen upstairs and downstairs, and it doesn't need to be pretty: It just needs to work.