I think Gerards idea to piggy back an established event would be the easiest thing to organise and going to somewhere central with cheap flights and easy travel is essential. I really think Sydney would be the go as Jetstar and Virgin have cheap flights to Sydney from most parts of Australia (apart from maybe the WA brewers).
I think having to hire a car and drive to another location adds and extra expense and time commitment, while choosing somewhere like Sydney makes it logistically a lot easier for everyone, plenty of accomodation, other things for people to do if they so desire. Get in, get drunk and get out kind of thinking.
If you piggy back something then obviously as stated one of your day events is already organised, if there were some keen members in Sydney they could perhaps look into hiring a venue/resterant/function room (maybe attached to a recognised good pub or brewpub) where we could have an AHB gathering for the night. Then maybe depending on numbers of attendees one or a few of the Sydney brewers or brew clubs could host a BBQ lunch with some of the various club members brewing some beer on their equipment.
I don't think there is any need for the travellers to brew, but if they can bring something along to share then good. I'm happy to watch, talk and heckle the brewers
Maybe either the club would like to put on some of their members beers (we can all throw a few $$ towards the costs) or buy a few keg of LCPA etc.
I think the idea is a good one, but I think to work it needs to be as easy to organise as possible, flexible in regards to it's ability to accomodate a range of numbers (possibly unknown numbers). Just some of the ideas I have listed could work quite well with 12-50 people.
If I am still around at the time I'd love to make the journey and be part of it.
Cheers, Justin