Hi
I did this tour in 2013 and had a fantastic time, the optional trips I would recommend that I did were Freemantle in Perth, the Kuranda skyrail from Cairns is a must as is Sydney's Blue Mountains and the Sydney Harbour Cruise is something you must do, you'll have an amazing time, I also did the bush bbq and the western Mcdonnell Ranges, I didn't do any optional's in Melbourne as I just wanted time to chill and wander round the city
we went via Singapore but I have been to Dubai and there is plenty to do there, i'm sure there will be an optional or two offered for you to go on or you could team up with others and book a taxi tour or just chill out on a beach
any questions just ask
Dave