Sorry, this might sound boring, but it just occurred to me, looking at a world map, that Western Australia is bloody big. We all know it takes up a third of Australia, but in world terms, it's a major chunk of land.
I have just checked the numbers, and if it seceded* and became independent, it would be the tenth largest country in the world. Smaller than Kazakhstan but bigger than Sudan. It's bigger than any country in Africa. Fact buffs will be thrilled to learn that Australia (6th) has such a big lead over India (7th) in area that if WA left, it wouldn't make any difference to their rankings.
*In 1933 68% of Western Australians did vote to secede. This failed to go through when everyone else pretty much just ignored them.