Did a v brief trip a couple of years ago and would def go back to Fraser Island.
Top highlight was Eungella National park to see the Platypus in the wild. (have a great range of nessie like shots as they are most active at dawn and dusk and move blooming quick!)
Would also go back to Barrier reef. We squeezed in a day trip from 1770 (town between Bris and Mackay) to Lady Musgrave Island. Fantastic snorkeling with turtles.
Driving isn’t bad but can take a long time. Do look at interior flights for big distances.