After an appallingly long delay (longer than two months!), during which I fretted about the difficulty of fixing my broken laptop (but also learned to ride a motorcycle in my vastly expanded free time), I finally caved in and found a local repair shop (warning: link will resize your window) who would take the case. They did a great job of soldering a new (ad-hoc) connector to the motherboard for me. The power button worked fine when the machine was returned to me.
Unfortunately, I'd broken the keyboard's ribbon-connector when I'd been taking the thing to pieces and putting it back together again, and the repair outfit had done the best they could with the broken cable I'd left them. Only about a third of the keys were working, so I called up the repair shop and ordered a new keyboard, which arrived the next business day. After all my experience taking the damned thing to pieces, I now rate myself at such a basic job as PowerBook keyboard replacement, so I opted to do it myself, and after an embarrassing false start, having forgotten to remove the remnants of the old broken connector from the socket on the motherboard, the new keyboard is installed and working perfectly.
Um, we now return you to your regularly scheduled 8020.