AS usual, a few comments expanded as I looked into the issues :-)

I don't like to rain on your parade, but I must mention some serious problems I have with your text. There seems to be something of a romanticising of poverty; e.g. This is not good advice:

One of our group was an Environmental Health Officer for a Scottish local authority. Most of the places I ate in or bought food from would have been shut down by environmental health in the UK. Flies all over the place, raw meat left out in the open air, food left over the heat of a fire for hours. Outside, cutlery and crockery unlikely to have been cleaned with anything more than dirty, day old soapy water.  I never got ill once, the food was gorgeous and incredibly cheap and very quick to make. The more run down and battered looking the stall or the bar, the better the quality of food. People are more likely to get stomach upsets from the spiciness rather than from food poisoning.

 What's the evidence for the last claim? You were lucky that you didn't get ill, many do, some seriously, a few die:

Diarrheal diseases(*) have been a major public health problem in Thailand for many years(1) (see Figure 1). Food is considered as a main route of transmission of microorganisms causing diarrheal diseases. There are approximately a million cases of acute diarrhea reported each year, and the reported cases of food poisoning are more than 120,000 per year(2).
...
The most recent report from Bureau of Epidemiology indicates that there are 146,325 cases of acute diarrhea; 2,421 cases of dysentery; 17,128 cases of food poisoning; and 797 cases of enteric fever (4 deaths)(2). (Data from 1 January to 29 March 2004)
The investigation of these reported cases show that consumption of microbial contaminated drinking water and food is the major cause of the diseases in Thailand. Diarrheal diseases are usually found among those living in poor environmental sanitation and those with poor personal hygiene. The disease incidence in children under five years of age is also reported high.

http://www.fao.org/docrep/meeting/006/ad703e/ad703e00.htm

And the Thai government has intervened to impose regulation, which you seem to be opposed to, but which may have helped you avoid illness.

An effective epidemiological system focusing on active surveillance on food borne diseases in the high-risk areas has been implemented. Thailand has a special team composed of epidemiologists, sanitation personnel, health education personnel, and personnel from Department of Disease Control, working cooperatively in both district and provincial levels to effectively prevent and control the diseases. This team will give a prompt response to investigate the source of diarrheal disease cases and/or outbreaks, and try to control the outbreaks within 10 days(3).
`Programme for Prevention and Control of Diarrheal Diseases' is aimed for the reduction of morbidity and mortality rate of the diseases, especially the incident rate of diarrheal diseases in children under five years of age.

Ibid.

Similarly I think your example of happy family life is also to be discouraged:

 This picture sums up my favourite aspect of Bangkok; it's social nature, food being cooked on the streets on little stalls, the bustle of the markets and the contrast it brings to those overfamiliar Western regulations and sterility. It wasn't unusual to see an entire family including young babies all piled onto the back of a motorbike.  It was rare to see anyone wearing helmets.

Maybe you'd have changed your mind if you'd seen one kid with his brains spilled over the road.
There was a programme in TV recently about Nigeria and the increased use of motor-bikes and the lack of traffic regulation and a local surgeon spoke about the increase in victims of traffic accidents, about 70 % (I think he said) were those on motorbikes. I'm sure that if the Thai parents had a choice, they would prefer that their children were transported in cars which conform in recent safety standards - or better still, good public transport systems.

Your idea that regulation leads to a "sterile" culture echoes corporate propaganda against regulation, especially in the US, which gets in the way of maximising profits. Even in the UK food is still far from "sterile":

The Consumers' Association (CA) has launched a campaign for safer food - as food poisoning cases continue to rise. There has been a four-fold increase in reported food poisoning cases in the last 20 years. Last year 97,000 cases were reported.

But the CA, which surveyed 1,000 members of the public, says the problem could be much worse as many people fail to report their illness. This could be partly due to the fact that some food poisoning bugs can take several days to take effect - so by the time the patient feels ill, they cannot pinpoint a cause.
There is also concern that doctors are failing in their legal duty to report all food poisoning cases to the local health authority.

The CA estimates that the real number of food poisoning cases could be 30 times as high as the official figure. It says the fact that so many cases go unreported mean that the food industry has been allowed to get away with bad practice.

http://news.bbc.co.uk/2/hi/health/912496.stm

To be fair you do mention the possible role of poverty :

If the Western world developed a climate like Thailand's over the next few decades, we wouldn't be able to adapt and live and work with the climate in the way that they do. We'd hide inside in air conned offices and shops and houses, air conned SUVs, and continue to deny the need for a change in lifestyle.  It made me wonder if poverty forces people to adapt in this way though.

Well, yes, rather obviously poverty does force them - in many of the hot and "poor but happy" countries, and I'm sure that most of them, given the chance, would opt for refrigerators, air-con, etc., just as the Chinese middle classes in the hotter areas of China are now doing, thus adding to climate change problems.

The poverty aspect might have become more evident if you HAD seen something of the sex tourism in the country :

The internal traffic of Thai females consists mostly of 12-16 year olds from hill tribes of the North/ NorthEast. Most of the internally trafficked girls are sent to closed brothels, which operate under prison-like conditions. (CATW - Asia Pacific, Trafficking in Women and Prostitution in the Asia Pacific)
...
Experts fear a resurgence of commercial sexual exploitation, child prostitution and human trafficking across the region because Thailand's economic meltdown has doubled unemployment to more than two million people; pay cuts have reduced living standards for millions more and the government has cut social security funding. Experts warn conditions are ripe for sex traffickers - "job brokers" who sell women and girls to brothels in Thailand and overseas. ("Survival the name of the game," Bangkok Post, 3 July 1998)
...
Close to 300 million dollars is transferred yearly to rural families by women engaged in prostitution in urban areas, a sum that in many cases exceeds the budgets of government-funded development programs. Between 1993 and 1995, it is estimated that prostitution in Thailand produced an annual income of between 22.5 and 27 billion dollars. (Dario Agnote, "Sex trade key part of S.E. Asian economies, study says," Kyodo News, 18 August 1998)

http://www.uri.edu/artsci/wms/hughes/thailand.htm

Even the particular variant of Buddhism, it has been argued, has played a role, as well as the Thai government's economic policy:

The traditional emphasis on polygamy in Theravade Buddhist society is said to have fostered the widespread practice of commercial sex work in Thailand today. Polygamy was outlawed 1n 1935 but ist still practised today - formally through men having more than one wife and informally through visting CSWs ( Commercial Sex Workers). Thailand's current economic development model has also served to institutionalize sex as a commodity and womens bodies as easily obtainable objects of consumption.

http://www.hangoverguide.com/over/factbook/th_sexindustry.html

And, what a surprise, US foreign policy played an important role too:

The Vietnam War (The American War)

The enormous scale of Thailand's sex industry today is largely a result of the American War in Vietnam. In the 1960s US Military bases began to proliferate in Thailand, and many young women were induced into the sex industry by their families and profiteers, as the high demand of US servicemen coalesced with the needs of Thailand's impoverished villages - eventualy leading to the acceptance of prostitution as a source of income for young women.

ibid.

Maybe it's because I'm a Londoner - that I moved to Nice.