In 1 and 2 (and also, "Thank you so much!"), the 'so' is only emphasis. But it should be heartfelt. I remember hearing a non-native speaker say, "Thank you so much" for something that was really just a small favour, like passing the salt or some ordinary action like that, and it sounded like sarcasm, because the thanks was too great for the help. So be careful to save the emphasis for times when it is genuine, because more emphasis is not the same as more polite.