I'd say the gold coast would be likely only due to its tourism, other than that the sydney opera house or the sydney harbour bridge would be way more likely, and due to sydney's population transport would also make a good target..
yeah i think it would take a lot of bombing to bring down those structures though so hopefully they wont realise that. it'd be pretty easy to de rail our trains, they do it well enough on their own. my friend found a dead body on a train here once, no one even noticed it, kinda makes you think