I only just came across this old post by John Wilkins publicly asking why he was not asked to speak at the Global Atheist Convention in either 2010 or 2012. See the whole thread on Wilkins' site.
I've got say that I find this kind of public complaint unseemly, as a general rule, but maybe that's just showing my age - I grew to adulthood in the 1970s, which was a turbulent time in its way, but I suspect that we were socialised to be more self-effacing than is the case these days (mind you, Wilkins is about the same age as me, so I'm not claiming that that's a difference between the two of us, just that my attitude to things like this may seem old-fashioned to some of my readers). [Edit: See comments on thread - John apparently misunderstood the format and has since sort of recanted.]
Be all that as it may, Wilkins has a very good article on secularism in The Australian Book of Atheism, and he would have been a good speaker/panelist. I hope that the committee takes note for next time.
More generally, there's some scope for fine-tuning the mix of speakers. E.g. - people that I've been talking to have been questioning why so many speakers are flown in from overseas (presumably with their fares paid), when there are outstanding speakers available in Australia. It's not as if there's usually a huge amount of reciprocation (though in my case, I did get flown to Orlando to speak to the Moving Secularism Forward conference ... so I can't complain).
For myself, I wonder whether it wouldn't be better to make greater use of panels, rather than lectures. Panels can vary in quality, but so can lectures.