Paul, many years ago I was told the story of the night buses, I think it may have been at a LURS meeting, probably in the late '80s. It was much as your version, involving the same three groups of workers, porters, printers and dockers. All three were in decline, at least in their traditional locations, the buses were little used, and consideration was being given to withdrawing them. The major difference in the story I heard was that one route was surprisingly found to be well used, but on investigation it was found to be not the traditional users, but young night clubbers who were using it, and this led to the introduction of new routes serving non-traditional areas. I don't know how much truth there is in this version.
I normally seldom use night buses, but did so frequently for several months during the Summer of 2000.
At that time all routes served Trafalgar Square, where there was a travel information point, I think it was in a vehicle parked in the square. Some of the routes vere heavily used; I think the N8 was one which was, and the N25.
Much has changed, not all routes now serve the square, and there are now less N-prefixed routes, and more 24 hour ones. It was a very good network when I used it, and it would be a pity if that is changing.