Which city is the conference in?
Quantas and its subsidiaries used to have a discounted air pass. Go over to Flyertalk and see if it still exists or what those very frequent flyers would recommend.
I have been three times. Off the top of my head:
We pushed a wheelchair around the Sydney Zoo. It is built into a hillside. There was an elevator to take us to the top and we worked our way down. I think we were able to see most all the exhibits.
They ferry system in Sydney is good. We actually just rode it around and treated it like a harbor cruise.
We stayed at a apartment hotel called 2 Bond St. It was easy to get to the historic Rocks area, the Opera House (not wheelchair friendly), the ferries, and the Victorian arcades. There is a Woolworths across the street with a good selection of groceries. With the time change we wanted to be able to fix food at weird hours and to save money.
Cairnes is very flat and has a lovely paved walkway along the sea front. It functions mostly as jumping off spot for the reef and the rainforest. It is not a massive city and we rented a car to get into the countryside. There is a nice cable car that takes you over the forest and to an artsy town. From there you can take a historic train back down.
Brisbane is laid out along a river front. There is a Koala sanctuary there I think called Lonely Pine. It has a nice selection of indigenous animals and birds. There is a large enclosed area where you can wander through free moving roos and wallabies. They sell a food like goat kibble and you can hand feed them.
The commuter train in Brisbane can take you to Australia Zoo (Steve Irwin’s.) That was a very nice facility too. My younger daughter idolized him as a child so it was meaningful to her.
From Brisbane we hopped a cheap flight to Magnetic Island which is off the coast at Townsville. It was very easy to rent a car and run around. My husband was still in his “OMG the wildlife will kill us all” phase and died when we got into the water. We all made it back.
We then took a 4 night cruise on a local small ship company called Coral Expeditions. It was very laid back but we couldn’t have gotten any closer to the reef. The snorkeling was fabulous.
My most recent trip included Tasmania which was gorgeous. I barely scratched the surface by visiting Hobart, Richmond, winery, and the penal areas. My great great great grandfather had been stationed there in the British army back when things were awful. The history presented to tourists is very honest about the impact on the indigenous people. I would really like to get back there and go into the mountains.
Melbourne looked lovely but my visit was colored by the oppressive January heat. I cannot say much except for recommending the aboriginal art gallery.
Every community has prominent memorials to WW1 and they are very moving.
Canberra and Perth were 30 years ago and I cannot pretend to know what they are like now.