Dennis,
Avalon is really two events in one. It is primarily a trade show for the aviation & defense industries. If you want someone to repaint your 747, provide a new missile system for your Blackhawk helicopter or supply you with aircraft tugs for your C-17 fleet then Avalon is for you! If you are looking for a replacement canopy for your T-6 then you will probably be out of luck. It is trade-only for the first 4 days.
An airshow runs for the final 2 days and is run as a seperate event. Naturally there is a lot of cross-over and there are more general airshow vendors available on the public days (model aircraft, museums, t-shirts etc).
The airshow has a good Australian military presence, and usually a substantial US military presence. The RAF and RNZAF usually send a plane or two, and other regional airforces might send something. Manufacturer attendence depands on what regional contracts are available. e.g. if one of the local armies were replacing their medium-lift helicopters then most medium-lift helicopter manufacturers would have some examples on display.
Vintage and warbird operators have been largely ignored by the airshow management in the past. You don't sell lots of new aircraft services to people who fly an old plane. In recent times they have brought the warbirds more into the fold.
Warbirds are now based within the main area of the show. They are protected by barriers so you can't walk right up to them. You can generally get reasonable photos, but probably not from the angle you want. Backgrounds will also be cluttered in the static dislay area.
Warbird attendence has been low in the past for two reasons. Firstly they weren't treated well by the airshow management, and secondly because Australia is such a big place that only aircraft based in Victoria could afford to attend. Now that the warbird owners are being shown a bit of respect they seem more open to attending, and there are a large number of local warbirds now (Temora, Tyabb and Wangaratta are 'local'). you will probably see 4-5 Mustangs, a couple of P40s, maybe both Spitfires, Yaks, Harvards, Hudson, Connie, Catalina etc.
The warbirds do display during the show.
I can't comment on the gold passes. I've never bought one, because I like wandering around the venue and I like to get down on the fenceline near the threshold for landing & take-off shots.
http://www.airshow.net.au/index1.html
Hope this helps.
Cheers,
Brett