I don't really see a major advantage one way or the other based on your situation.
I'm assuming your 1000 users is the max attendance at the event / inside your coverage area.
1000 users with a 30% take rate will be 300 associations
Assuming even distribution of APs and Clients:
300 / 12 = 25 users per AP
with 75% on 5Ghz that would be 19 on 5Ghz and 6 on 2.4Ghz
300 / 8 = ~37 users per AP
again 75% on 5Ghz that's 28 on 5Ghz and 9 on 2.4Ghz
Based on those numbers I'd agree that you are better off with more channels available.