I've found that dressing appropriately and professionally helps out at least somewhat, both in getting new students and working with others. I seem to get a better response when dressed professionally. For some strange reason, wearing shoes rather than sandals seems to make a difference.
I've heard a few Thai people mention that they treat Thai teachers in a more traditional fashion than farang teachers (I take part of this to mean that you can make the occasional cultural blunder and Thai people will understand), which has its advantages and disadvantages. However, dress seems to be tied in with class and maybe to dress the part brings you a little closer to being viewed as an 'ajahn' rather than a goofball.