I did much to learn it, formally including reading and writing which helps tremendously to get the phonetics right. It took me 3-4 years to be comfortable to the point of reading without even having to think about the correct pronunciation. I have to say, not bragging about it, that I'm very good at languages (I'm very familiar to fluent with several).
With all that, I lost interest and motivation over the years because:
- as you say, most Thais we encounter speak a version of the language which is extremely different from the official Thai.
- most do not have anything interesting to contribute to any discussion which goes beyond the stage of "it's hot today" or "is the food too spicy?".
- in Isan (my wife's region), and certainly in the villages, many people understand Thai but can hardly speak it. I'm not kidding! My wife has to accompany her elder brother to the hospital, recently, because some doctors cannot speak the local "phasaa isaan", and he cannot speak proper Thai.
- I worked a few years in a Thai enterprise, with mid-high class Thais who spoke proper Thai. They hardly interacted with me socially, many quite obviously hated having a non-Thai colleague around.
With all that, I lost interest.