to the phoenix , It's going to depend on what you want to do. 2 weeks is not a long time, and the IP, even straight through, is going to take several days. It is a great trip (in GK class), and the scenery from SYD-PER changes dramatically through the trip, (so I'm told, haven't done SYD-ADL leg), though a large tract of the Nullarbor is same-ish. thadocta's recommendation of visiting wine regions near Adelaide is a good one (Barossa, Adelaide Hills and McLaren Vale being the closer ones)..some nice BIG reds to be had there!

Alternately, you could hire a car in SYD, and say, drive from SYD-MEL-ADL, and catch the IP from ADL-PER. The coastal roads take longer but are more picturesque then the more direct routes. Could be a little rushed but I think any route you have in the 2 weeks is going to be so.

Driving by coast: SYD-MEL: 2 days MEL-ADL: 2 days (you could easily take 3 days each for these). Allow an extra day or so each to explore MEL and ADL (and PER) attractions. I think that'll see your two weeks through!

Anyway, down to you. A common traveller's fault (and I do it all the time) is to try and cram too much in...better to see fewer things in the allocated time, you can come back and see the rest another time.