I do think you run the risk of cross-over and the largest class will likely pull the sailors to it.
That is the downside to such an event. Granted there really isn't that many people who have to make a choice, but it'd be nice to not have to make that choice. Racine there was maybe 4 teams/boats that do both classes.
Mostly I say this out of pure selfish-ness as I want to do both the F16 & F18 Nationals next year.