Well! In between taking care of the convalescing laurie_robey, prepping for AnthroCon, doing commissions, and (oh yeah) working on my regular day job from home, I've also been e-mailing back and forth with the Spinrite devs about the particular mode of failure, and they came to the conclusion that my DVD burning software was goofing up on what it was supposed to burn from the .iso file created. So they pointed me at a free utility that would burn the DVD properly, and as of tonight, I now have a working bootable Spinrite disk.
So I'll set that to run overnight, and we'll see what (if anything) it can do. I don't expect it to make any major noticeable improvements in my system's speed or whatnot, but if it will keep the disk alive longer, I'll take it.
Anyhow! Another thing crossed off the Too-Much-To-Do List. Woohoo!