If you're looking for flat water - Queenscliff in Victoria has a lovely enclosed bay. I've only been there once or twice but is a really nice place to ride. Look out for the rocks at low tide though.
As for good spots in and around Adelaide for flat water. Milang on lake Alexandrina is a great spot on N, NE, SE, S. Parham is about an hour north of Adelaide up the gulf and is one of the best flat water locations. It's a bit of a walk out if you get the tide wrong but just on the turn of the low tide is best as it can be a tad choppy at high tide. It works on N, NW, W, SW, S. Check out :
www.facebook.com/pages/Parham-Kiteboarders/271479522914169?ref=ts for photos and info on Parham.
Jess