I am finally (tempting fate) declaring this project to be a success. MythTV is running well, and old recordings & rules restored. My SVN repos are all back up with intact histories, and today my bugzilla database has been restored in all its glory.
Satisfyingly, instead of simply restoring the user filestore, above were laboriously restored from database backups that are created on a nightly basis using home brewed cron jobs. So at least I can now be confident that my backups actually work and really do save the required data.
I have yet to decide what to do about the ML kernel issue, but that is not urgent or pressing. I have looked at CentOS Plus kernel and while I don't
think it will resolve the problem I encountered, I admit I have not actually tried. I would rather come back to that question once I have decided whether or not I want buy any new DVB tuners, as the new tuners might 'move the goalposts'.
Many thanks, especially to B'Cat, for assistance.