Would be happy to meet up in Sydney. If you need any info on the Blue Mountains can suggest some day walks / overnight walks or could even take you abseiling, canyoning or caving.

The VIC / NSW coast road (Princes hwy) passes through some great places but is a much longer route than the Hume hwy. Given that you will be spending time on the Great Ocean Road you may prefer something different. The Victorian and NSW alpine areas are a much more interesting alternative and not all that much longer seeing as you are planing to come back via Canberra. Much of the alpine areas in southern NSW and northern VIC have been affected by bushfires this season. If you are interested I can do some research and recommend some areas that were not affected. The Hume hwy between Sydney and Melbourne is the main route but is rather boring especially as it has been so dry this summer.

The Jervis bay area could be worth a visit with its fantastic beaches, walking, canoeing / kayaking and good scuba diving. Camping in the area is available in the Booderee National Park.

If you make it to the Barrier Reef (which you probably won't have time for) scuba diving is fantastic. The Yongala ship wreck is the best dive I have ever done, assess is via Townsville. Snorkelling is probably good too.

Let us know if there is any thing you're specifically interested in.