Hey Kiwi Mike,
Loving the report! Sorry you had a mob scene at the Mont St Mike. It may well be the most touristed attraction in France (maybe after Tour Eiffel?). When I first went some 10 years ago, it was in January and there were very few tourists and most of the shops and restaurants were closed. Was there again in October '13 and the crowds were huge. Sad to no longer be able to simply drive up to it and park, but I understand that the existence of the causeway was ruining the hydrology. Best way to see it, I think, is to either go early in the morning or late in the day during tourist high tide, or hit it in winter some time.