I can't give you figures, but there was a sizable pre-European aboriginal population of Australia, much more than what most people think. They mostly lived in the temperate, wetter areas of the East Coast, not the deserts where a lot of people normally associate their way of life with. It's just that lots of them got wiped out by disease etc., and the survivors were usually the most isolated ones, in areas Europeans couldn't settle.
For a POD, perhaps settlement of the East Coast by East Asian or Polynesians?
Of course they would have to get there somehow, and I cannot think of a plausible reason why they would choose to go to Eastern Australia and settle.
This would also make the native Australians (predominantly) not aboriginal.
Alternatly you could have agriculture and metal tools traded with East Asian peoples and spread south-east into the more fertile parts of Australia. Domestic animals and subsequently disease may also follow, resulting in a larger aboriginal population, and one better suited to deal with (ie survive) the European settlers.
The result of such a native population?
Well, I think that the European settlers would still see the aboriginals as very primitive. Their contempt towards them may be lesser if they see they have more advanced tools than OTL and perhaps a greater population. But only marginally.
A larger number of Aboriginals would survive into the 20th and 21st century, would they be more a political force? Perhaps, maybe following the example of the Maori people in New Zealand, and demanding a return of their old lands and reperations etc.
Even an Australian Aboriginal Treaty of Waitangi?