Spent a couple hours with the Product Recovery CD, and repaired my installation a little. Immediately notable effects: logging in to the ISP was near-instant, rather than a drag of about 8 minutes. Well, near-immediately notable. One also noticed that on immediate attempt to log in, the modem was not detected, and that an attempted joggling of cords brought about a memory dump and restart. But after that it was all good.
If this were a client's machine, I might have just gone for the easy and known good "Save all the files you care about to your backup here, and let's reinstall!" But I like my system, thanks much, as much as I am intending to reinstall soon.
Plus, it would have been a son of a bitch to save everything.