When you checked all the plugs, did you check the connections were making contact with each other? As the plugs may have been wet to begin with, but when you pluged them back into each other, did any of the contacts bend or break? Also if you are not using your bike over Crimbo it might be worth sticking your dash in the airing cupboard to make sure that there is no water in that (not in an area thats too hot). Sorry it's a bit long winded, but its all I can think of?
have to admit it sounds more like the clocks themselves. does the actually speedo and rev counter themselves work and its just the small screens that dont work. if its the clocks themselves id take them apart and leave them to dry out somewhere warm.
otherwise if you fancy a bit of a run out im just outside boston and also have a 99 model so we could swap things over from one bike to the other and try isolate the problem.