Anyone who cooks knows that even one ingredient, however small, can make or break a recipe. Fans of Jamie Oliver, the British chef, know this well. His cookbooks are full of simple recipes, and often the finishing touch is an herb such as fresh rosemary or a fresh red chili, without which the finished dish lacks its wow factor. He also lists "optional" ingredients in many of his dishes. But leave them out, and it's just not the same thing.
And that's why Thai food tastes better in Thailand than almost any restaurant elsewhere. It's largely about the ingredients and how fresh they are.
On my first visit to Thailand, I stayed at the Mandarin Oriental Hotel and ate several times at their lunch buffet. Now you'd think two things: one, hotel food is hotel food; and two, especially, a buffet can't be that authentic or good. But it was a revelation. At the time, it was the best Thai food I'd ever eaten, whether in Los Angeles, New York, or anywhere else. It just tasted fresher and more complex.
Later, I took a cooking class at the hotel, and although it was years ago and I don't remember much, I do recall that the variety of ingredients available in Bangkok was nothing I'd ever seen at an Asian market stateside. I find that a lot of Thai food outside of Thailand just tastes the same. It's too sweet, under-seasoned, and sings just a couple of notes.
Earlier this year I had a chance to revisit Thailand (Chiang Rai, Phuket and Bangkok) and I explored a couple of open-air markets with Surachai Kakaew, executive sous chef at the Anantara Resort Chiang Rai, where they also give cooking classes. What I discovered was what I suspected on my previous trips: it's the ingredients.
In the markets I saw six different varieties of eggplant, several different kinds of basil, and countless types of chili, many of which I had never seen the likes in Asian food markets back home. Go to a market in the US and you'll find one kind of ginger. Here I saw three. There was Thai garlic, similar to what we get at home, but not quite the same, as well as a type of parsley I had never seen before. There were even a couple of items that even the chef couldn't identify. Not only is there more variety, but I suspect that the ingredients are fresher than they are when they travel long distances to New York or even LA.
You might ask why aren't these ingredients available outside of Thailand. "It's partly climate," chef Kakaew explained, "and partly demand. Some things grow better and more economically in our tropical climate here in Thailand, and if there's no demand for a wide variety of ingredients in the U.S. there's no incentive to import them." So while you might be able to find some things in, say, Los Angeles if you look hard enough (lemon grass, kaffir leaves, etc.) you won't find everything you'll see in a typical Thai vegetable market.
All of which is to say, if you love eating, if you love Thai food in particular, it's reason enough to visit (that and, of course, the people, the culture, the scenery, the wonderful massages for next to nothing, and the shopping).
I did find, sadly, that the North American propensity for making everything sweeter than it needs to be has seeped into some Thai regional cooking. If you love cooking in general or Thai cuisine in particular, taking a Thai cooking course makes a worthwhile break from sightseeing. Many hotels offer them to guests, and Bangkok's Blue Elephant Cooking School (it's a popular restaurant as well) is well known and reputable with small classes and morning or afternoon sessions. The Amita Cooking Classes (http://www.amitathaicooking.com) also come highly recommended. Both offer a great meal and perhaps a chance to meet fellow travellers with common interests. But most importantly, it's an opportunity to experience authentic Thai cuisine and to bring back culinary skills that will last a lifetime.