mmm345, thank you for putting the time into this, I really appreciate it.
So one last question - In your example, I follow it all, but isn't the critical link still the airport itself? Say I depart to Cessnock from Bankstown, on a beautiful clear day, just after dawn, in winter, no fuel for an alternate, No cloud on the GAF at LSALT plus 500 for the final segment, therefore I can navigate happily but when I get to Cessnock there is a fog bank. For a reason like this scenario is why I interpret that General statement at the start of the Alternate section of AIP to be if there is no TAF you need an alternate.
Taking it to an extreme, say I was chartered to fly an A380 from Sydney to Cessnock (yes I know the airfield wouldn't take an A380 but its just a hypothetical, I couldn't imagine doing the flight without having an alternate that has a valid TAF.