Haven't read the whole thread, so maybe it has already been mentioned, but QF gives everyone the international allowance on domestic flights connecting to international flight, and on all domestic flights if you fly in/out of Australia (not sure if it has to be QF or Oneworld or if it is for all airlines). So while there isn't a Oneworld Emerald benefit of increased baggage allowance -- you must have QFF status to get that -- there is this "tourist" allowance that should help you.

As for renting a car in Sydney, it is a negative for touring the city, and parking is incredibly expensive (e.g. $85 for 3 hours at MLC center, next to the Westin), even street parking is metered in the touristy areas and costs a few dollars per hour (plus the hassle of feeding the meter). For a 2 day stay there is more than enough to see within walking distance and by ferry, even the Explorer buses are not really that necessary.

Must try in Sydney are the Sydney rock oysters (Tweed river), some of the best in the world. Great seafood in general, even at cheap restaurants. Miso (japanese) in World Square has some great cheap food (my favourite is their deluxe sashimi bento box for $15, better than some sushi places costing 500% more).