Only just saw this thread. Yes, we did go in April (for my Son's bucks party - not quite as feral as it sounds).
Flew out in a Chieftain - let someone else do the flying.
Last minute decision to drop into Betoota on the way proved to be one of the highlights.
Birdsville fuel was about $3.80/lt if I remember rightly.
Probably about 10 or 15 maybe 20 non-local aircraft overnighting including a KingAir, a Conquest and a number of Caravans.
No camping under the wing but stayed in tent-city with 2 man tent, bedding & chairs provided.
Bloody hot both race days. About 39* both days.
About 1800 people at the races. A good crowd for atmosphere but not too crowded - no queueing for a refreshments!
Pub not too packed at night which allowed people to get around and chat to those that had flown and driven in from all over the country.
Great atmosphere and a lot of fun was had by all.
All up cost for 7 of us was $2300.