GBR, especially Lizard, sounds like a wonderful beach vacation -- but is it more than that? We have been to Maui several times -- how is it different?
We have never been to Australia or New Zealand, and have only 2 weeks to spend, so we want to get the most out of a little time.
How much is possible in 2 weeks? We have a meeting in Sydney for 3 days, then another week to do -- what?? Counting travel days from LA, 2 weeks seems not enough time, so we have to make some choices.

Maui and the GBR could not be any more different.
Do some research on the GBR on www.google.com.au and look up Lizard, North Queensland, Tropical North Queensland and Queensland resort Islands. This will answer any of your question I am sure.

Maui is a large volcanic island in the center of the Pacific Ocean, battered by the full force of open-ocean waves; creating deeply eroded shorelines and beaches. You can climb to the top of the tall wide volcanic remnants to view lava flows, craters, and extensive views. It is a popular and easily-accessible vacation destination, so the island is ringed with high-rise hotels, condos, restaurants, and other tourist trappings.

There are few islands on the Great Barrier Reef large or tall enough to support habitation - Lizard Island is one of them, but it is tiny (about 2mi x 3mi), and much of it is parkland, so you will have a far more remote experience in the single luxury resort. Much of the waters surrounding Lizard, and the GBR in general, are protected by the system of GBR reefs, so you rarely see big waves.

Besides the GBR is about 1200 miles long. The number of resort islands is between 10 and 20, I would guess. So compared to Maui, you have a lot more variety to choose from. Some islands are actally right on the reef while most of the resort islands are "continental islands", lying in between the reef (which averages 40 or so miles out to sea) and the mainland. The majority of resort islands have just one resort on them, another contrast to Maui. The adjoining mainland of Australia offers a lot of different things to see and do as well (rainforests, waterfalls, wildlife, etc). The whole experience would be very different to staying on Maui I'm sure.

Also, in Far North Queensland resort towns like Port Douglas and Palm Cove, hotels are not allowed to be built higher than the tree tops. The absence of high rise buildings makes a difference.

Hamilton Island in the Whitsundays has high rises, but my understanding is that many islands off the coast of Queensland do not permit the building of high rises either.