A more interesting scenario is this If you have a 5 boat fleet... say... Hobie 20's... How many of those sailors would tell the single P19MX or Nacra 5.8NA in the area to stay home or go sail by themselves. You could tell him... Hah... we have 5... go sell yours and buy mine and we will have 6.... But that is not likely to happen.... (Hell next regatta you may only have 3 20's.) If you don't consider the sailors on the left over boats .. the end result of one design would be one less sailor to contribute to the local racing scene.
So My quesiton would be... which do you enjoy more.. a larger competitive fleet or a small one design fleet.
The Hobie 16 class in the mid atlantic is very active and quite competitive. However... to be compettive you need to have a small team of 300 lbs or so. This year.. they will try to revive interest by splitting out a payload 600? class for teams and boats that are a bit on the heavy side. Why would a large one design fleet split out the heavyweights and split their class????
Well for one reason... the heavy weights won't come out to play any more.... Its not competitive and its not fun (and they haven't bought a suitable boat for their weight). So... by recognizing that maintaining competition under a new set of rules may grow participation they have made a positive step forward (but it ain't one design).
Back in the day... the huge numbers of sailors were in the B and C fleets ... Those folks raced and enjoyed the competition... They did not have to train to keep on racing or feel compelled to move up. (do you think they would have been upset to race in B fleet against a P16 or a N5.2 at the time)
My point is that fleets need to favor real competition more so then real one design standards.
So... the question is not Is one design more fun... Rather its Does your strategy (Payload 600, Catfight, Formula, one design) keep the racing competitive and people interested in racing.
Final note... There is an emerging trend to develop Personal handicaps for fleet racing. (Much like golf handicaps.) the idea is that by creating competition in the fleet you will spark and revive interest.
Matt Bounds noted that lots of people stopped racing after they grew tired of watching him and another guy walk away from them.... Personal Handicaps might have kept every one in the game.... Not just Matt and the other guy.
Once again personal handicaps ain't one design... (even if everyone is on your favorite boat.. the TheMightyHobie18) It is all about generating competition.