Here's a link to the Sydney based clinic I'm looking at
Has anyone found DEXA scans useful and easy to integrate into a nutritional plan
Started by James Hall, August 21, 2013 · 2 Replies · 3,021 Views
DEXA gives you a rather accurate starting point, as well as intermediary ones if you wish to. 
They're good for giving you lean bodyweight (IMO the vast majority underestimate how much fat they have), as well as muscle mass and bone density readings. The lean bodyweight reading can be a good reference for body composition goals. The muscle mass over time can also be good feedback.
I don't know how you'd integrate it into a nutritional plan. It can give you an RMR but even that is an estimate based on height, weight and gender.