Log file was useful, but fairly technical - I could not see any specific line that explained my apparent crash. however, I think I have got to the bottom of it...
Following extensive file housekeeping and a CD ripping session, I performed 'auto import' on my entire music library NAS. The new files were correctly imported and file analysis began as the last part of this process (I now better understand what file analysis does). It is at this point that MC gives the impression it has crashed (rainbow spinning wheel and no response to mouse clicks) plus the Mac OS reports MC as 'not responding' if you run Force Quit.
However the NAS was still happily churning away to itself, so I assumed something must be happening and left it to run. After several hours I returned to MC, which was now responsive and showed a message along the lines of "analysing 3000 out of 31,000". So MC does not crash, instead there is a period of 'deep thought' during which it gives the impression of crashing. I had simply been impatient, although if MC had properly warned me it was about to go into a death-like trance, I would have arrived at a different conclusion and gone off to do other things for an hour or so before panicking and pulling the plug.
It's still running now - problem solved, I hope.