Well, after a delay, I decided it was time to upgrade, and failed both with the "Comfort" upgrade process and the manual method. First, the env stats:
MYSQL: Ver 14.12 Distrib 5.0.92
The system lists a stack of files that it claims (a) exist (they don't) and that are (b) read-only. Short output snip below. The ComfortUpgrade script omits the leading server name (in this case "/kunden") but a manual inspects shows that the individual files themselves don't exist. Since the upgrade script requires this to be fixed, no other info available.
Complete disaster. After a couple of database errors (of the ALTER TABLE flavor and seemingly not of consequence) the script simply stops after displaying a series of progress dots. Example below.
Comfort script output
Checking existing LimeSurvey files...
Warning: The following files/directories need to be updated but their permissions are set to read-only.
You must set according write permissions on these filese before you can proceed. If you are unsure what to do please contact your system administrator for advice.