Dave,
I'd have to say one of the things that made a difference with the class in Sydney was having suitable water for tunnel racing. While you guys are on the Torrens this might be an issue for the smaller A O/B tunnels but would be better served by the 30+ inch hulls.
The other thing that made a difference in Sydney was developing an attitude within the club where the experienced racers help out the newbies to get things right the first time, and trying to make it as fun as possible, rather than saying "you should have bought an XYZ" or "that class sucks" etc.!
The boats are out there - it's just a case of looking after the people with them when they show an interest in racing or even joining the club. They don't want to be told their boat sucks or whatever, they want to race it against other similar boats.
Almost all of the guys racing A O/B tunnel at our club have been racing for less that two years. It's no secret that this timing also corresponds with moving to the new pond and a change of attitude within our membership.
I think what you have done by sponsoring the class at the BotB and now at the Winter Spec, along with this thread on IW, has encouraged these newer club racers to be interested at racing at a higher level, and to diversify into other existing classes.