I learned some Thai my first year here. Tuned in, and tuned right back out.

Self-sufficiency Thai for urban living shouldn't take more than a book, a CD, and about 4-6 weeks.

Living in the sticks or going bamboo takes a bit more effort (maybe).

For the fully incorporated entrepreneur types with Thai employees / suppliers etc you probably want to learn as much as you can.

Don't go to a school to learn days of the week, numbers, etc. You can learn that at home with a laptop and headphones.

Be aware that your ability to tune out junk will gradually disappear.