I've only been to one World Championships where the Fleet size was over 100 (124). That was back in 1994 at Lee on Solent (Southampton UK). They didn't split the fleet just the results. I finished 55th and was seventh in the Bronze Fleet but my now wife and I won the World Novice Championship prize so we were both extremely pleased with our performance.
I think it's a good idea to split the results into fleet prizes, it can only be good thing for the Class and future competition.
I totally agree that 90 out of 100 don't expect to win that's why having a silver fleet or perhaps an amateur fleet could prove very popular.