As others have said, the policy is irrelevant. To access the lounges in the international terminal, you would have to clear Customs to enter Australia, then clear exit Customs to access the departures area and the lounge (which you can’t do without a departing boarding pass). Then there’s no ordinary way to get back into Australia once you’re in the departures area of the international terminal. So it’s far more difficult than getting a gate pass to clear security at a US airport (which isn’t trivial in the first place).
If SYD is your final destination, my suggestion is to use the public showers in the international arrivals area (as others have said, they’re perfectly nice, just BYO soap and towel; I’ve used the ones on the check in level, one level up from arrivals) or go to the beach (seriously), dropping your bags at your accommodation first if it’s accessible (which you should be able to do even if you can’t get into your room until the afternoon).
Note that if you have a domestic connection on VA, you can certainly access their (very nice) lounge and its showers in the domestic terminal.