Further tests, which involved slowly transferring song folders piece by piece, uncovered a corrupt .wma file. Might be possible to have Rockbox throw up a "corrupt file" error rather then crash/force a reboot?
Still really wish I had known about the Fuze back when they were being made. I've gone through so many Clip+ models over the years but the Fuze beats it hands down. At this stage it's highly unlikely to ever see a new one appear in the wild.