Just for a few moments, I'm going to take a different attitude to this thread (this is NOT how I think, but I think this is worth bringing up)
Every single person PAID for the event, and therefore, they are your clients. If you want to have repeat clients, you don't tell them that their feedback and thoughts are not welcome. You listen to them, you take them on, and in the MINOR areas where you get the most feedback, you can do it even better next time.
Now that I have done that, I will go back into my own opinion.
I know how frustrating it is having people complain about how you do things, whilst they are not willing to atually do it themselves. I did three years of committee for Corvettes of Melbourne (please note, I do not speak on their behalf in this instance as I am just a member now), and we all have to listen to people complain about how we do everything yet never offer any suggestions about how to do thing better or offering to help us to do things so they can be better.
No one in this thread is really complaining per se or saying we could have done soooo much better, the response is majorly positive.
Feedback like this is NOT complaining, it's just feedback.
You can either get up in arms over people having an opinion, or you can think "We did a great job, but here's where we might be EVEN BETTER"
Your choice.