You can access the Domestic Business lounge if you are flying Business but aren't Platinum - we did so in SYD a few weeks ago.
Other benefits of Gold would include better chances for points upgrades / Op-ups coming through, complimentary Qantas club membership and the like, and access to international OneWorld Business class lounges when travelling on OnerWorld airlines.
There is a lounge in ASP:
Fly - The Qantas Club - Lounge Locations - Australian Domestic
Hoping to visit it myself next month!