The rates you have quoted do not strike me as particularly high either for Sydney or this hotel particularly when they include a decent continental breakfast in the executive lounge (for golds).
What the rates end up will depend on demand but they are worth regularly checking particularly in the days immediately before your stay. Further, the differences between guestroom and plus, deluxe and plus even executive and plus are minute and, in my opinion, certainly not worth paying for. You would be very Iucky to get an upgrade to a suite or even a relaxation room both as a gold and for a week stay. I like the relaxation room but not at that price. My advice would be to take the AARP rate and keep watching the situation. Alternatively, look elsewhere outside the Hilton. Enjoy your visit.