I agree, the afterparties were awesome. Some sponsors really stepped it up (i.e. provided beer), and the fun increased accordingly.
You guys, the organizers, also seemed a lot more relaxed than the previous year. I'd imagine you're getting things dialled and that's nice to see.
I think once summer rolls around, people start going away or get busy with the race season, which is probably why attendance drops. The spring races serve as a tune-up following the winter which could explain their popularity. But it seems a lot of the best of the racers stop coming as the summer goes on. One possible option is to keep the spring dates, take a break in the summer and resume in the fall. I'd bet races right now would be quite popular since the calendar is pretty quiet (though you're fighting daylight). Maybe consider weekend mornings when the days are shorter.
I also thought having the races every 2 weeks was better, though I was bummed when I had to miss one knowing it would be a full month between races for me.
The courses were great, but the Stairs to Despair BP stage could be used more sparingly (though I could rip it with my eyes closed now having raced it so often). I think some people were scared off by some of the harder stages (like Ladies), but it is fun to have the opportunity to race those. I'd also like to see more longer stages, like a full 7th-Leppard-Crinkum-Kirkford-Griffin to go along with Ex-Dreamweaver. Also, the Seymour dates were fun and more races there would be great, maybe split evenly with Fromme (which would help with avoiding Stairs to Despair).
Overall, I had a great time this season and apprecated all the hard work. I'm looking forward to next year.