I wouldnt put much faith in those little bonnet deflectors. Mine broke on the way from Alice to darwin last week & it done more damage than a little rock would.
A good tip on any long drive up here is to keep an eye on the roadkill. If there is a bit on the road generally the live ones arent far behind. Also the big wedgetail eagles that are feeding on the dead ones take a long time to get airborne when they are full. Having one of these come through the window is worse than denting a bonnet on a roo.
Also check the fuel prices before you leave & plan your fuelstops to the better prices. Some of the Roadhouses are up to 30c a litre different from the nearby towns.