While obviously certain areas are better than others for observing wild reptiles, you also need a hell of a lot of luck as well to actually find anything. I spent just about every school holidays bushwalking through the Royal National Park looking for reptiles but more often that not you could spend the whole day looking and not see a single snake, while other days see quite a few. I think some people have visions of these magical places that only one or two herps know about where there is a diamond python in every tree and a death adder under every log. In all my time herping I've never come across such a place(certainly not around Sydney anyway).I've spent days in perfect diamond python habitat, where they certainly do occour, and not seen the slightest sign of one. My advice to anyone wanting to see herps in the wild is to go invest in a good pair of walking shoes and a map of a particular area and go from there. There are two great books, bushwalking in the Sydney region vols 1 & 2 which have some great walks in them on which you are probably a fair chance of seeing something reptilian.
There is a great walk out of Stanwell Park (south of Sydney) that takes you through some really spectacular rainforest, potentially perfect habitat for lots of different types of reptiles. I did the walk in winter, but am planning to do it again once the weather warms up a little so if anyone wants to tag along they'd be more than welcome.