In that amount of time you could probably get to Townsville (through Brisbane) and back, or to Adelaide (through Melbourne) and back. Or you could go to Brisbane and spend some time there, or to Melbourne and spend some time there. I really like Melbourne and the wine country around it, usually went there directly rather than to Sydney on my Australia trips.
Roads are mostly connecting coastal cities. Think of it as coming into Baltimore, where can I go if I have only US-17 or I-95?
Get on an Australia tourism site. See what interests you on the east coast. If I had just nine days I would probably go to Melbourne (first choice) or Sydney (second choice) and stay in the local area. Waste as little time as possible long distance driving. From either place, you can get up into the mountains. Or visit the other.