It has always been my view that the only way Australia would be threatened with invasion is in the context of a World War.
It is not like China would just randomly decide to invade Australia one day and not invade anywhere else. We have no real territorial disputes and no land borders.
So we are only under threat in a World War situation and if that happens our allies will choose to defend us if it is in the broader interests of the war effort, or let us fall if it isn't. That is how it was in World War Two.
Sucking up to America beforehand will not change that dynamic. They will only defend us if it is in the interests of the broader war to do so. Sucking up to them in the decades beforehand will not count for anything.
We should pursue a policy of armed neutrality. We should have nukes.