Hasn't been posted in a while. Full credit to OP Peanut money in the deal post a couple of years ago.
I've yet to try it. I've heard that it's pretty good for a free lounge if you can get in. Hey, free food is free food.
Below is the list of all eligible cards, bold means unlimited access (or JV is trying to say something). Otherwise, you get two entries per calendar year. Your two entries can be used in the same visit for a guest to access the lounge.
Some reviews:
https://www.ausbt.com.au/american-express-amex-sydney-airpor…
http://www.pointhacks.com.au/reviews/american-express-sydney…
http://viewfromthewing.boardingarea.com/2015/06/29/review-am…
- Eligible Cards
(a) The Cards listed below that are current and issued by American Express Australia Limited and American Express International (NZ), are eligible to enter The American Express Lounge with the exception of internationally issued American Express® Centurion and American Express® Platinum Cards, which are also eligible to enter the American Express Lounge:
American Express® Centurion Card,
American Express® Platinum Card,
American Express® Business Centurion Card,
American Express® Business Platinum Card,
American Express® Corporate Platinum Card,
American Express® Qantas Corporate Platinum Card,
American Express® Explorer™ Credit Card
American Express® Platinum Reserve Credit Card,
David Jones American Express® Platinum Card,
Qantas American Express Ultimate Card,
American Express Velocity Platinum Card,
American Express Airpoints Platinum Card.(b) The Cards listed below that are current and issued by licensed network partners are eligible to enter The American Express Lounge:
ANZ Frequent Flyer Black American Express Card,
ANZ Rewards Black American Express Card,
Westpac Altitude Black American Express Card,
Westpac Earth Black American Express Card,
Commonwealth Bank Diamond Awards American Express Card.
You could probably bring a total of 7 people in that way :P
There's no reason/incentive for you not to use your unlimited access on your Plat Card, so only if you had more than 3 people would you use up the entries on your other cards
Or.. see if a random person wants to go in - maybe you could sell it to them for $20 lol (i.e. just get them to give you cash)