"What are we thinking - that there'll be a ground war in our backyard big enough to worry us but too small for the Yanks to care?"
The big question in my mind is does Australia need to be able to strike at the Chinese mainland on their own? A " land based, mobile, long range strategic missile capability (5000kms +) conventionally armed." isn't going to work - if you are in it with the USA any ICBM will be assumed to be N tipped whatever you say, If you're on your own that's a very expensive delivery system with the effect of the V2 campaign on the UK in 1944/45 - irritating but pointless. You fire 100 missiles and hit about 100 hectares of China...............
And any non -nuclear war that only affects Australia without the USA will be fought in Indonesia, the Philippines or in the S Pacific. I can't see the point of a high end bombers like the B-21