If you're getting too many fake smiles, you might be in the wrong place. Try moving out of the main tourist areas. I can understand how difficult it is for Thais to put up with all the Indian and Chinese tourists, and plenty from the Middle East and Russia. They have to deal with them all day long.
I asked my Thai gf, who works in a 5-star hotel in Pattaya, if she likes them. Graciously, she replied, "not too much" LOL
Why am I still here? I like it here and don't want to start over in another country after 20 years, even if there might be some advantages. I've never been to Vietnam and don't have a desire to visit. I don't believe your story that in Vietnam they smile genuinely all the time, and that they aren't after your money, and that they really "dig" all foreigners. The desire for money is universal around the world.