Australia, New Zealand & the South Pacific - hotels in Australia and Thailand

From my previous travel experience I know that one usually finds a better deal than what he had, once he arrives at his destination. Seasoned travellers, do you think it is a safe bet to NOT make hotel reservations for Sydney and other cities in Australia and expect to find something reasonable once I get there? The same question for Pattaya, Thailand.

Thanks for your responses.

Sydney happens to have a glut of hotel rooms (a legacy of the Olympics) but that doesn't mean that you find a cheaper hotel when you are there in person (often the cheapest is via the web, sites like wotif.com). But there are weeks when every single room within 50 miles is sold out in Sydney (don't ask me how I know this) and you pay triple for any last-minute bookings. It seems to happen surprisingly often in Sydney. For the rest of Australia doing what you suggest is far more viable (possible exception of Melbourne). No idea about Thailand except that local (not international standard) hotels are 20% of the price but may not be good enough.