Dave, it can get pretty bad in some places, the Tanami Road (Track) is well used by Campers and Road Trains, the corrugation on this is not the best......
From Darwin to Halls creek your on the sealed highway sharing it with the likes of the above mentioned vehicles and Police....lot's of them.
From Halls Creek to Alice Springs is where the fun starts, then afterwards the Old Ghan Route is even more interesting!
From Port Augusta to Adelaide your back on sealed highway and once again, shorter versions of Road Trains called B-Doubles occupy the road (Third trailer cannot be attached south of Port Augusta) this is a busy highway with all sorts of vehicles including the local Police who really love the speed freaks !
Your not going to see many Police through the Off -road sections so this is where you go flat out!
As for Roo-Bars and all the extras, the choice is up to you mate......you either hit a Kangaroo or you don't, that's what it's like, you can be lucky or not.......don't do what a lot of tourists do and swerve to miss the animal because this is when you can get into real serious trouble.........