Wrong, there would be no huge demamd for International flights wanting to land after 11pm or take off before 6am. They would be happy with some flexibility under the current rules.
Most of Europe have curfew restrictions, and whilst SYD is no LHR, it is still just as reasonable for a curfew to be in place.
Domestically, there would be a bigger desire for flights within the curfew period. But not to the point that the ecoomy is loosing Billions as a result of it.
(if your arguement had any weight, then ALL your other arguments about the airport price gouging {which are 100% correct} fall over. )
That being said, the issue is not the curfew, it is the-:
Noise sharing Runway direction requirement,
The Use it or Loose it requirement of the hourly movement cap,
The Inflexibility of the curfew period.
The runway direction should be most appropriate based on environmental conditions.
If the airport movements are restricted for some reason due, then the airport should be able to catch up those lost movements over the subsequent hours. Personally there should be no Cap at all, and the Cap is where the airport is losing money.
There should be a flexible 1hr period either side of the curfew to ensure unforseen circumstances do not unduly ground a flight overnight costing an airline $100,000's. There could be very clear guidelines about how that flexibility can be applied.
ie: aircraft goes Tech during a turnaround, it can be fixed and still depart.
ie: An aircraft scheduled to land at 6am is running early due to winds, shouldn't have to hold and waste fuel (burn those aweful CO2 emissions) because the environment allowed the aircraft to fly faster.
ie: weather in MEL /BNE restricts movements due to their runway configuration. If a "scheduled" flight is late through no fault of its own, it can continue to SYD. Instead of sending the aircraft around on late final cause it wont touch down untill 23:00:05 local time.
When has common sense and logic ever prevailed in life.