We purchased the see Sydney card pre trip as I have been to Aus before and the see sydney card is a must for your visit to Aus.
There are so many attractions that this can be used for you just run out of time.
The opera house tour I have completed for the 3rd time and never tire of this tour.
We also went to the Blue mountains the cost of the train fare is additional however is minimal and well worth the trip. We had a lovely day in the Blue mountains Ledra is a lovley little town. The cream tea is a must absolutely fabulous.