This is NOT the biggest museum you are ever going to see. In fact, it's downright tiny. The small admission fee ($5) helps support the work of the Royal Flying Doctor Service however, so pony up (and throw in a bit more while you're at it). You will see an informational video, and learn a great deal about this important service.
I honestly didn't get the impression they'd turn you away if you DIDN'T have $5, but the service certainly deserves at least that much support from you.
While the vast majority of people in Australia live in the cities, that only encompasses about 20% of the land mass of Australia. For the other 80% of the continent, you have people who may be living 400 kilometers from the nearest doctor. The RFDS is how they get medical help.
At the Visitor's Center you will learn something about the history of the service (the founder is on the Australia $20 bill), and what they do on a daily basis. You will see an early peddle radio and the sort of emergency medical kit that is out on the stations even today. You will get to board a retired service plane, and talk with someone who can answer any questions you may have.
It's not the most exciting exhibit you will ever see, but it may be one of the most inspirational.