I've got my name down! As always.
There were plenty of S30s last year actually (a number of which went on track) - we were just over the other side of a hedge from the majority of the cars in the stand area.
Thing is, Japfest at Castle Combe is a long way for most people to go - and calendar-wise is very close to the Samuri Gathering at the much more central Donington Historic Festival - which is obviously pretty much 100% S30 exclusive. That might be a factor. It also might be that the scene that Japfest exemplifies doesn't necessarily appeal to all S30 owners - whereas something like the Donington Historic does.
Which reminds me - personally I think the club should make a much bigger push to have a good showing at Japfest 2 at Donington. As I alluded to, that location is central for just about everybody - to me it makes more sense than focusing primary efforts on the Castle Combe event. I shall be aiming to attend Japfest 2 should the club have a stand. That's my tuppence-worth anyway...