People will appreciate you and look at you differently
As tourism is such a big industry in Thailand, people will see that you are a foreigner and tend to look upon you and treat you as a tourist. Once you can speak Thai, local people will view you in a totally different light. They will be friendly and curious to get to know you. Showing that you can speak Thai will demonstrate that you have put an effort into integrating into their country. Thai people will be very impressed when they hear that you can speak Thai.