Good news. I checked my System Restore and discovered that restore points
had been made yesterday evening for both the installation and the
uninstallation of the Windows Installer Cleanup Utility. Noticing that I
also had a routine system checkpoint that had been made seven hours
earlier, though, I chose it for doing a system restore. After the restore,
AFAICT, all changes had been rolled back to the way things were yesterday
morning. And when I tried OfficeUpdate, it worked! It even had a
PowerPoint update for me, which I downloaded and installed. So it appears
that I'm, relatively easily, back in business via System Restore.