and get multihulls out at the same clubs participating and contributing.
This seems to be the required "first step." If multihulls become a regular part of every sailing/yacht club, then we have a chance to grow the multihulls. I'm not sure that sailing, as a sport, isn't a "net zero" sport, i.e., we aren't growing the number of sailors. Getting into the yacht clubs might increase the number of cat sailors.
Overall, however, getting kids sailing in anything is a good first step to getting them on beach cats. They don't have to start on cats, IMHO.