I think it is hard to overstate the importance of individuals inviting people on their boat to expanding the sport. I can't think of many people that got into sailing, let alone cat sailing, without being invited to sail with someone else. This should include both friends and family. Cats are enough fun that just bringing someone out on a recreational sail will frequently hook them. I used to have my old roommate crew on my F18. Now he owns his own H16 and wants to buy my F18 to race. Some German tourists that I met on the beach and took out sailing have now switched from a 470 to an F18.
One of the down sides to relying on a yacht club to bring in youth sailors is that most of them will be children of members. Unless yacht club members are having 3+ children that all end up sailing as adults, this is not a way to grow the sport.
However, yacht clubs do provide the social aspect that is important to growing sailing. A lot of Hobie fleets do a great job at having a lot of fun at regattas too. Friends and family are more likely than strangers to feel part of a social group than random strangers showing up at a yacht club to learn to sail.
On the question of families sailing... I got into sailing by crewing for my dad on a H16 for two seasons. Then, I wanted to be the skipper. So, we got an old H16 and me and two of my other 9 year old friends (that also used to crew for their parents) went out racing against the adults. A couple years later, we split into two teams and were in the middle of B fleet. By high school we were in the middle of A fleet. There are now two boats sailed by third generation H16 sailors with the parents still racing and the grandparents still involved with it. So, it does work.