For Sydney, we like the Sydney Inter-Continental. It is made from the old Treasury building. very close to the quay, views of the harbor. the biggest plus is that if you book an executive room (not much more at all than a regular room) you get limo service to/from airport and a great breakfast spread in the executive lounge every morning.
saves much more than the extra you are spending for the upgraded room.

for the great barrier reef, i compared Hayman and Lizard island resorts on this thread.
http://www.flyertalk.com/travel/fttr...ML/000006.html

HAVE FUN!! and if you do not scuba dive, get CERTIFIED and dive the great barrier.