I've sort of done that kind of thing, one time doing a loop driving from Melbourne to Adelaide and back, and one time a loop driving north from Auckland, staying at motels each time. I made a point to visit national parks and similar places for dayhikes. No deep outback, though.

I suppose a tour can be good, if you find one focused on your interests, rather than just "see the highlights of Australia in ten days". I find I spend too much time waiting for the rest of the group doing shopping when I go on group tours. Something more focused, like a birdwatcher's tour, might avoid this problem.