You can't really blame AmEx for that though. Lounges get whatever space is available in the international and I doubt AmEx would outcompete the duty free tenants who pay top dollar to get the prime real estate in the terminal. At the same time, the Centurion lounge isn't in a bad location either, particularly if you have a flight departing from that wing of the international terminal. Keep in mind, not all of us fly Qantas out of the international terminal (indeed Qantas doesn't fly to many destinations like Europe and much of North America, a story for another day).
I will concede that the spread was very basic, even by AmEx standards (c.f., the Centurion lounge at LAX or SFO). My understanding is that these overseas lounges at SYD and MEL aren't operated by AmEx directly but by Plaza Premium (take that for what it's worth).
Having to go to a bartender to grab booze is an AmEx policy, apparently as this is also the case in the domestic US lounges as well. Whether it is top or bottom shelf liquor I'll leave that up to you. What I will say is the Centurion lounge at SYD makes a great appetizer before heading to the Emirates lounge (remember you can access that lounges flying QF/EK if you are QF Gold and not travelling to the Americas) which tends to have limited hours to put it mildly.
As someone with Crohn's disease, I can assure you that it's always a hope that our bowel movements can fit into such a glass at times! 
