I personally think a Raptor would be an amazing fit for Aussie World, that way you've got a kiddie coaster, a family coaster and a thrill coaster. This would round it out pretty nicely tbh. Maybe then add one or 2 more flat rides that are thrilling as most of the flat rides are more family thrill (Dark Rebel, Redback, Mozzie Musta etc).
If Sea World hadn't built Vortex, a Top Spin would have actually been pretty high on my list of rides that would suit the park but probably a smaller one built by Moser or similar as I don't think Aussie World would fill up a 40 seater ride very often. As far as Flat Rides go, I'd put in a proper drop tower (Maybe a S+S Combo drop to differentiate from Batwing or one of the Sky Jumps from Intamin). For a flat ride I'd go maybe one of the park model Mondial Top Scan's like Knotts has. However I'd have it run a halfway decent cycle at least. Could be themed to an Aussie Windmill or something lol.