I would be more likely to attend over Labor Day, although it has other
drawbacks, and I'd have to see. Possibly the timing has to do with featured
artists' schedules.
I do think that a fest in April isn't enough time to build the event up
properly. There aren't that many thereminists apriori, and with that small a
pool, I think that without excessive notice you can't get people to commit
to attending. No one is sure that anyone else is going to come and no one
wants to end up holding the bag for reservations and transportation on a
cancelled event.