I understand the Op, it does come as quite a culture shock if some sort of appreciation is not forthcoming, more so if our western upbringing ingrained the 'thank you' as being almost automatic and sincere
I do get thanks in the shape of a wai from people, and actually find this rather embarrassing, same as the gentile subservient style of water pouring by family at songran, my son throws out a wai when he returns from school every day, I am not comfortable with ' elevated' status, I prefer, and do get from my family the occasional thank you
However returning to the Op comments if we are going shopping for groceries and I hand my wife 10,000 baht, seldom a thank you just straight into the handbag, so have removed this little irk by having her take money from the machine at the supermarket ????
I think lack of showing a little appreciation at appropriate times could well hamper farang Thai relationships, as surely no person wishes to be taken for granted.
Just my thoughts, no biggie, as I say my kids are polite that makes me proud