yeah gidday Jim,
distance from Adelaide to Darwin is a bit like Tijuana to Vancouver, and Brisbane to Perth is like Frisco to Miami so distances are sizeable.
There are a lot of good suggestions above.
One of my favourite travelling weeks was spent in Victoria - a day to do the Great Ocean Road pub crawl, a day trip up to Mildura or Swan Hill (sample some local wines), another day eastward to the Alps (snow), spend a full day there, loop back from Hotham down through the hills Buchan (caves) over to Lakes Entrance (wet a line)- this is where you strart to bite into another week - leisurely drive south through Sale, get over to Wilsons Prom', spend the night in Philip Island, next day over to southern end of Mornington peninsular, ferry across Port Phillip Bay back over to Bells beach - depending on the time of year you've just gone from surf beaches to desert to snow to lush undulating hills in a little over a week.......and you get four seasons in each day for free ...most of this is "on-road" but you may be able to grab a another day and a local guide to get dirty with
