I hate it when people talk them up like they were hell hardcore.
Yes, they were invaded. But so what? So was pretty much every single society throughout history.
It is accepted that 'Normal' societies grow, develop, innovate, and progress. Even if it takes thousands of years, they will eventually progress from Nomadic lifestyles, to Agricultural, to Industrial, etc.
While they did have somewhat of a 'legal system', and language; I doubt that this would have ever have been improved upon.
I think if Australia was never invaded, then the Aboriginal society would have just remained the exact same today as it was back then. I don't see how it would have moved forward in any way.