Wow, NYBanker, thank you for your detailed comments and suggestions.

As you suggested I am probably going to spend most of my time in Port Douglas while in Cairns area and come back into the city late afternoon on my last day to do a quick tour of the city and for overnight before my early early morning flight to AYQ.

With many comments favoring a longer stay in MEL, I was actually able to book a flight earlier than what I had before via Alice Spring that would get me into MEL at around 3PM (leave AYQ around 930AM). This gives me an evening in MEL city and to walk around.

I certainly am looking forward to the QF F lounge in MEL. I remember the SYD F lounge being one of the best I have ever been (and probably still is one of my top three lounges) but had only 30 minutes there as explained earlier. This time around, I am going to budget in about 3 and half hours for spa and formal dinning.