If you're from NSW you are referred to as a New South Welshman, and I agree a sydney resident is a Sydneysider not a harborsider. In the context of footie rilvalry NSW are "cockroaches" and Qld are "cane toads".
I've always understood sandgropers for WA to refer to their land in general, and especially farmland, being very sandy.
Residents of Melbourne are indeed Melbournians, and I would refer to someone from Brisbane as a Brisbanian, I've heard residents of Hobart referred to Hobartians, I don't know if this is the accepted term though.
..observation would suggest you add the suffix most easily adapted to the name in the following order of preference
1. -ian
2. -ite
3. Who named that city?...just make something up! (this applies to Sydney, goodness knows what you call someone from Port Macquarie but you can bet it only involves the word Port, discard the Macquarie part.)