Corrente returns, now with happier hamsters!
As matters turn out, it's extremely difficult to fine tune a server when it's crashing all the time. Who knew? So, yesterday I gave up the unequal struggle and purchased some more RAM.
The site had been running smoothly most of the time, but when things went wrong, they went viciously, horribly, and above all time-sink-ingly wrong; I want to be blogging, not system administering! So I hope the RAM stabilizes matters.
UPDATE Adding... Long-time Correntians will remember a similar shakedown, though perhaps not quite so brutal, when we upgraded to Drupal 6. Those problems died away too. Crossing my fingers that history rhymes....