Hi guys, my 2c worth from an 80`s windsurfing freak background :
One-sided mylar/dacron laminate sails were the first experiments using this technique to create a sailcloth that wouldn`t stretch as much as Dacron alone, the fully-battened surf sails were taking a higher load than the "Windsurfer One-Design" sails. I don`t know if it was developed FOR windsurfing, but they were probably the earliest users of this cloth.
All sails made of this cloth had reduced stretch, but their lifespan was short-lived, because the bond between the two would fail due to the dacron side stretching more than the mylar side, cuasing delamination.
The newer mylar sails don`t delaminate, don`t stretch, and if you go with the right weight sailcloth they will last longer than your sailmaker / sail supplier would want them to. (Ask your sailmaker what cloth he would recommend, and go one heavier )
If your class rules dictate that the old one-sided mylar MUST be used, get the class rules changed, because your sails will delaminate after a year of hard use. It`s not the build quality, it`s the cloth that is at fault. I`m shocked any sailcloth company still makes the stuff.

I don`t know what the process is to approach Hobie to have class rules changed, but I`d imagine that if all the sailors agree to it, Hobie would change the rule. If I know them, they will still be the only official supplier - that`s a business decision and I`m not knocking it, but they would still make money either way. (In fact they would stand to make more since all the competitive racers would invest wisely in a sail that will last them.)

Unless, of course, Hobie still have 400 tons of that cloth in a shed somewhere, and need somewhere to offload it....

Cheers
Steve