ill agree with this but you are starting to make an epic long trip.
Also consider taking the train home from Adelaide. Its quicker, you can relax and i assume going back is alot more boring cause you just passed everything not too long before.
EDIT:
Or another idea would be to fly to Melb rent a car and do some of the above drives. something like
>fly in and spend a couple of days exploring the city (goto the zoo, we love it!)
>rent car and do day trips to yarra valley etc
>over night trips? sorrento (check out the old ww2 base) then ferry across to bellarine peninsula to check out Torque (bells beach/rip curl/quicksilver shops?) stay somewhere over night around there then back to melb via geelong (Warrabee open range zoo on the way into melb) then spend another couple of days drinking epic coffee and exploring the cbd (arts centre, museum,HM Thearter for a play etc).
Hmm think i miss Melb/vic been a while since i have been there, lol.