Queensland by ship or by sea

I need your help. We are currently booked on Solstice for a Great Barrier Reef cruise for March 2017. We're debating switching this to a land trip in September 2017.

Couple of reasons...sticker shock over Solstice excursions in Cdn and we would be forced to do cruise ship tours in a lot of ports due to tendering and schedules. ( eg...$350 for a outer reef trip vs $200 on a much better private tour) Time of year, I understand Sept/Oct would be a better time to go weather wise

We'll be doing Sydney and Melbourne independently but are considering dropping the 12 day cruise for possibly a week in Port Douglas and a day or two in the WhitSundays.

This is our first visit to Australia. Any advice?

If it were me, I would drop the cruise.

While I have not been to the Whitsunday Islands, I have been to Port Douglas 5 times. I think being on land will give you so many more opportunities to see and do things that being on a cruise will not. And, as you have already seen, the costs should be much less than what you'd spend on a cruise. Finally, going to Far North Queensland (the GBR region) is better in Sept/Oct than in March. One big factor is that stinger (deadly jellyfish) season runs from November to May. By going in Sept/Oct, you can actually swim from the beach and Four Mile Beach in Port Douglas is a very nice beach indeed.