I'm jealous! Hamilton Island is gorgeous! I don't know the resorts, but I'd recommend checking out some package deals and maybe treating you and DH to a few extra days. I know when we did our honeymoon up that way (many years ago now) that it was cheaper for us to stay 7 nights than it was 3 with the packages that are available. Anyway, however long you stay, you'll have a ball!
I wish we could stay for longer! We are heading to London and Ireland over Christmas so we are saving madly for that. If we were away for longer than 2 nights I'd want the boys to come with us and it's just so much disruption to them to only go away for such a short period of time.

However if we like it then we might go back again for longer as a family next year.