Not sure what the original construction was or whether you potted the magnets. I don't trust the nickel coating alone under these conditions. The steel/nickel interface is even more of a problem.

I am inclined to think that for this sort of environment galvanising of the steel discs is the way to go.

Regarding the other factors I agree with DaveB and I agree with Ron that superglue is one of the things best forgotten, It sticks paper but other things do as well. I see no use for it in this field.

I believe Hugh has had some luck with some form of bitumen/epoxy paint and that may be a way of keeping the problem in check with what you have got to deal with.

If you can satisfactorily protect the magnets without completely potting them I go along with it but potting may give better protection in the long run under these conditions. If you pot with satisfactory material I see no need for the stainless band round the outside but that is an individual choice. My concern is corrosion not magnets falling off.

 If the magnets were mounted flush to the edge of the rotors (as many still are) there was no way then (if bondo or similar was used) to keep the magnets from being thrown or at least kept from moving as there is tremendous torque on these trying to break them free.