According to my house's original owner, this tree is actually three trees (Pacific Dogwoods) that were transplanted from about 1000 feet away, from the land that is now Peninsula Park, prior to the development of the rose gardens there now. This makes the tree at least several years older than the house itself, which passes its centennial anniversary this year.
I've had a couple of arborists take a look, since a couple of the leaders are dead, and it's been shedding bark and dropping dead twigs for a few months. Both tell me that the severity of the pruning by the power companies, in order to create a clearance corridor for the power lines going through it, have opened up the canopy to sunscald, which is likely the cause of its present state of decline.
I'd like to save it if possible, of course, but the prognosis seems a little dire.
In the end, I think it might come down to cost. I'm following up with the power companies who have contracted past pruning efforts, to see what I need to establish in order to get them to kick down the cost of repair or removal, rather than bearing the expense myself.