Plumbing update: the tech came out & took a look at my leaky bathtub faucet. Nice young fellow, professional & friendly. I'm female & he talked to me as the homeowner instead of automatically deferring to the man in the house. (He did speak to my male housemate when I wasn't available for a bit, as I'd instructed.)
The verdict: pressure in my line is 25 psi higher than allowed per local building code. Solution is a pressure regulator valve near the main shutoff by the road. There isn't anything particularly wrong with any of the water fixtures beyond that, tho' he did change the cartridge in the shower control handles.
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So I gotta rustle up about $1400 to have the pressure valve put in. So there ya go.
The tech actually took pix of the various steps he did on the job, so I can see what he did, including a shot of his pressure gauge on my outside faucet. I don't feel like his company was trying to jack me, which is a Big Deal(tm).