by Buster Blocker.
DOH!
Turns out another undocumented land-mine was in play. The latest version of Moodle requires PHP v. 5.3.2, and our server was sitting at 5.3.1. Time for a trip to Upgrade-Land, and all should be well after that.
Ken, thanks for doing yeoman's duty here. Your extra set of eyes got me thinking beyond normal troubleshooting and that led me to the apparent answer. If it doesn't fully work I will report back as to what did work, but even so you are my hero!