You're being disingenuous. You only gave reasons why the US wants ANZUS. But why does Australia want it? You didn't say. No one stays in a treaty unless they get something out of it. So, what does Australia want from the ANZUS treaty even assuming that it's true that China will never militarily attack Australia? Does the US Navy protect your suppliers, your customers, your trade routes? Does the US Navy being there allow you to negotiate better deals? Maybe it's the money American sailors spend on shore leave there? What are the ANZUS reasons for Australia?
Partly historical - we've always stood with the US and, for the foreseeable future, will continue to do so almost certainly regardless of ANZUS or otherwise. NZ, for example, is not part of ANZUS because they won't allow nuclear armed ships into port and the US won't confirm which ships carry them. Both perfectly valid positions, so ANZUS was suspended in terms of NZ.
Do we derive benefits? I'm sure there's some economic benefit (US ships don't actually dock here very often, but the marines up in Darwin probably help out a bit). There's joint exercises (which include NZ, Singapore, and other nations in the region - not part of ANZUS or any formal alliance). There's cooperation on intelligence and other military matters which provide day to day benefits. Of course there's the benefit of a powerful ally should something happen and, whilst unlikely, it is still a tangible benefit. Of course, having the treaty doesn't actually mean the US would come to our aid - that's far more likely as a result of the overall relationship, but ANZUS (or any other similar treaty) certainly adds to it.
So, I'm not being disingenuous - I'm pointing out that constantly suggesting it's some sort of one-way street with no benefit to the US is demonstrably wrong and just silly. The value of the *relationship* with the US is far, far more valuable than ANZUS.
Oh, and to answer specific questions - no, the US navy doesn't protect our suppliers, customers, or trade routes by and large. The US navy isn't "here", and their overall presence has zero impact on our ability to negotiate trade deals (Trump pulled the TPP, but Australia still has very favourable trade relations with pretty much the whole of SEA and the Pacific).
Again, I think you have a very inaccurate view of the reach and impact of the USN this side of the Pacific. Obama wanted to increase that presence in response to China in last year of his term - Trump seems ambivalent in that he wants to pressure China but he doesn't want to increase presence (sending a CBG for a FONOP isn't really a general increase in presence).