Well, of course the Comcast phone tech's assertion was "It's the modem" (after he tried several times to sell me on a higher internet speed despite zero indication that I have insufficient speed for what we're doing here), but I pushed until they agreed to set up an appointment for a tech to come out, though he gave me three dire warnings that if they get out there and it's the modem, we'll have to pay a service call fee.
Fortunately the tech who came here heard me out (including the information from this forum), verified my cable modem model and age, and declared that he can't imagine that it would be the modem. He then evaluated everything from the street all the way to the modem, and while he didn't find any one big problem he found 9 different little problems that combined could have easily been the culprit: Several loose connections, a couple of corroded connections, a 4" cable segment, and a part that they stopped using years ago because it was the cause of various intermitten problems. He was so confident that it's not the Netgear equipment that he said that if the problem isn't resolved he'll put in the notes that they need to check the lines from even further back in our neighborhood .
So I haven't looked back at the logs yet but I'm happy with the service that I received today. Thanks again for all of your help!
