I rented a car in Sydney, drove to the blue mountains and spent the night- having a car to move around, stop where I wanted, etc was pretty convenient. (And we found a grocery store and wine shop....)
We splurged on a corner view suite at the Echoes Hotel- amazing view. Instead of hanging out with 300 tourists over at the viewing platform, we had a bottle of wine, cheese, olives and crackers and watched the sun set over the Jamison valley. In this case the room itself was an integral part of the sightseeing experience. In the morning, sunrise greeted us with parrots on the deck, and clouds settled into the valley- morning coffee as the sun dried up the clouds filling the valley. We were able to get going to Wentworth well before the first tour buses arrived. (which was a common theme at more than a few venues- beating the massive influx from the buses- uluru, katatjuta, Kings Canyon, Flinders chase, etc)
Some people dont mind sharing with 40 folks in a tour bus with bored guides yacking into a microphone...we tend to be much more solitary in our explorations. Hence two of you (or a family) in a car on GOR would be FAR better than spending one very full day with strangers... if you are wired that way.
Agree with uber in the city. Pretty easy in SYD
We were there for a month and rented cars 14 days, although all of this was well outside the cities.
HTH
Edit: prices were variable. 4x4s were basically 120-200 a day; a mid sized SUV in SYD for two days was AUD100 a day. Same car for 4 days dropped to $58..go figure. Prices varied based on pick up/drop off as well as length. We needed 4x4 in 3 locations so had to pay 650-700 for 4 days, about 200km per day allowance.