Situations and problems are different in different parts of the world and in different parts of the same country and even in different sailing clubs in the same region.
In your case if your club only has one 420 and all those kids, it sounds like a perfect situation for introducing a fleet of little cats. Hopefully, the "speed disease" would be contagious and spread like an epidemic throughout the other clubs in your area and then all of Australia -- and then to the rest of the world....well, at least in the PERFECT world, that is what would happen. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
However, I have my doubts that U.S. sailors are going to want to build boats.
In your case, if you have a team willing to build some boats, I think it would be a great idea to REQUIRE the kids who are going to sail the boats to be involved in the building process, so they will appreciate the boats and take care of them and try to avoid running into each and other and damaging them.
This has been a very effective policy at Larry Hale's Scout Camp up in the Florida Panhandle. They get old Hobie 16's donated to them, and the kids, both boys and girls, have to do most of the grunt work to renovate them and also the regular maintenance work.