Thanks for the response!
In the end, I just restored an image backup of my boot drive that I made before installing the HTC software. Magically, all the VR stability issues have gone, and the Windows wonkiness with them.
It appears that the HTC software was installing a filesystem driver (?), running as a service. The first clue was that stopping this made the machine a lot happier. However, the HTC uninstaller didn't work properly, so wouldn't remove the software.
Anyway, without the HTC software, just using the basic Steam VR drivers, the Vive works beautifully, and the lighthouse Bluetooth power management works again too- which is a net benefit. I also don't have a ton of random Vive-related processes running doing spurious disk I/O and unexpectedly snatching focus when playing non-VR titles (the latter cost me an Overwatch match or two!).
I guess the only downside is that now that the bundled titles are no longer offered as Steam codes, but are tied to the HTC software, I can't have any of them as promised. You really do have to pick your battles, though; a smooth and stable system is probably a bigger net benefit than a "free" copy of Tilt Brust and Everest Experience (though they do look cool).
Thanks again for trying to help, though- really appreciate it. It's nice to know that there's a human being reading this stuff.