No we didn't take an excursion as we are locals, but for overseas visitors there would be so much to see as you will dock at Circular Quay, close to the rail station and directly opposite the Opera House and almost touching the bridge. Ferries from Circular Quay to Manly or the Zoo, or Hop on Hop Off bus just through the railway station. Plenty of eateries if you walk from the ship and turn left towards the Opera House or turn right for the Rocks area. One of the best docking places in world I would think as it is almost in the city.
It is such a long way to town, we stopped over on a Sunday and some cruisers seemed disappointed when they got in to Brisbane on the shuttle bus and most things were closed. Not going ashore I can only say it is about 45 mins to the city and no taxi service available.