If you want to go well in them, then you probably should.
I would reccomend focusing on Prominent individuals/Social + Cultural features Post WW2/Australia's regional and global links/Aboriginals/Women's Liberation/Communism + associated wars/Environmental management - as these are probably the topics that will be focused on in the heavily weighted extended response. Just aquire some basic knowledge about these topics and you should be right.
If you really cannot commit, then just read over your study/class notes. It's only the School Certificate, it isn't too hard so I wouldn't stress about it.