I don't know about SYD, but in the USA it's typical that airports give priority for outbound elite status passengers, regardless of what they're flying. For BKK, where I fly extensively on many different carriers, I've never been able to use fast track when flying in Y before, regardless of status. That includes TG, SQ, LX, and previously OZ, all when flying *A Gold. My experience is that the fast track is only for premium class passengers, and even then, not always, being frequently inbound in TG on C I'm haven't had fast track access, but do sometimes.

When I was checking in for my flight, I saw this gold card the agent was filling out, and could only see the words, "Fast Track". At first I thought, "YES! ICN finally has added fast track service", only to see it was for arrival at BKK when she handed it to me. A bit of a let-down, but will still be great if it's consistent. These days I normally only fly C when I get an op-up, or if I really need to fly and Y is fully booked. So any benefit for having status when flying Y is appreciated.