I doubt that the fine for exceeding the speed limit by 5kph really is $350, but if it is then so be it. Keep to the limit, obey the law, and you have nothing to worry about. If you break the law and get caught then cough up, whether you think it's a cash grab or not. The same fine would apply to an Australian citizen as it would to a tourist.

I don't know about most people, but when I'm in a foreign country I'm more careful about sticking to rules (not just road rules, all sorts of rules) than when I'm at home. Crossing roads legally as a pedestrian, buying tickets on public transport, that sort of thing.