Rather than finally abandon the scanner I investigated a bit further starting with the one clue in 10.2.8 where Apple System Profiler correctly reported the scanner, but as an 'IOSCSIParallelDevice' off the Bus. I noticed that Panther had replaced the IOSCSIParallelFamily.kext in System/Library/Extensions with a new version (version 1.3.0 in Panther, version 1.2.4 in 10.2.8).
Suspecting that this might have something to do with the problem I replaced the installed 1.3.0 version with a copy of the 1.2.4 version and rebooted. Although the scanner is not reported in System Profiler it is now recognised by Scanwise and I can scan quite happily as before with no obvious system problems encountered so far. Reverting to this earlier version of IOSCSIParallelFamily.kext seems to restore this SCSI scanner's functionality in Panther.

