I've been to MEL and SYD. Compared to MEL, I think the SYD International J Lounge is very good. Natural light, and a view. Sure once you've experienced the FLounge it's terrible in comparison, but that's by design.If you thought SYD INT J lounge is bad, check out the MEL, DRW or CBR international lounge!
I do think though that what you get at MEL and SYD Int J lounges is not a good look for say paid J travellers to LHR when QANTAS Club members on the cheapest economy fares get a lot better at LHR ahead of the flight back to Australia.
As for the domestic lounges the HBA lounge is the worst I've been too by a country mile. Too small a lounge, not enough staff, very poor drink and food offerings, always at capacity when I've been there. It's a capital city and there are airports that aren't even capitals such as OOL and CNS with much better lounges.