I was thinking about this the other day, but basically you could have state themed areas, each divided into a couple of contrasting sub areas.
Might go something like this:
Queensland
Great Barrier Reef - Undercover kids area with small flat rides. The little mermaid area at Disneysea might be a good basis.
FNQ Rainforests - The E ticket ride here could be the Tully river rapids. It would start off as a typical rafting trip, but there would be a thunderstorm dark ride section that culminates in a "flash flood" and a final drop.
Western Australia
Nullabor Plain - An area themed like an outback airstrip and truck stop. The flagship ride would be a Soarin type ride in a hangar. Other attractions would be a few small kids flat rides, including a convoy ride. The main food outlet would be a Roadhouse.
Pilbara - Themed like an iron ore mine, the flagship ride here would be a large roller coaster dropping into an ore pit, a B&M dive machine or similar. The loading station would be like this, with a fully themed queue of catwalks around rock crushers and so forth
South Australia
Barossa Valley - Imagine theming similar to what you see on Furius Baco, but of course with South Australian sandstone architecture. Rides could include a drunken barrel ride, and an S&S freespin called "The barrel roll".
Murray River - Perhaps a river port, with a paddeboat ride?
Victoria
Goldfields - A Goldrush era area, with the flagship ride being a multi launch family terrain wooden coaster, similar to Grizzly Mountain at Hong Kong disneyland.
Farmlands - A fun farm themed area for kids, with a mash up of an orchard, dairy farm, with tractor rides, one of those carousels like the one at Alton with farm animals, a kids flume ride down an irrigation channel.
Northern Territory
The Outback - Could be a wildlife section with
Kakadu - Aboriginal Cultural Attractions
(Yes I'm aware I'm knocking off the back half of dreamworld)
New South Wales
Sydney - This might be the main entrance area, and would be a microcosm of inner sydney, with federation architecture, and a street of terrace houses themed around a street carnival.
Snowy Mountains - Flagship ride would be "Bushfire!" , a motion base dark ride where you join the volunteer fire brigade and head off down fire trails to face a bushfire at night.A small ski village area would contain family rides.
Tasmania
Dockside - Casablanca Place inspired area that features Australias maratime history. Could potentially have a splash battle ride around a port themed area.
Wild Forests - Tall timber themed temperate forest. Attractions might include a flume, as well as adventure sport upcharge rides such as coaster ziplines and ropes courses. There might also be an ATV coaster like Juvelen.
A family dark ride could involve a whimsical journey through a forest where you use torches to spot various native animals, with a score given depending on what you find.