Unfortunately there aren't many costal areas now that aren't being exploited into tourist cash grabbing locations. But the central to north coast is still a fantastic place to visit, your really missing out if you havn't gone north of Sydney! Pretty much anywhere from Lake Maquarie and up to Coffs is going to be shed loads nicer than Sydney
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Coffs is a good place to chill out, plenty of nice scenery around and pretty good surf. Ports alright to visit for a day or two. Moving further south Hawks Nest and Port Stephens are also ripper spots, as long as your not there in school holidays 'cause the tourist hoards move in.
These are all pretty quiet places without the big attractions that the masses drove there for like theme parks. Is there anything your looking for in particular or just somewhere quiet near the beach to chill? Or just either spending a few days in each locale or plonking down somewhere for a week?