Good comment/question. I generally try to err on the side of being more polite and gracious unless there's a reason not to, because I don't see any real downside to it.

Does that mean you think the politeness - effect curve is usually much flatter on the right side of the maximum (optimal politeness) than on the left?
Exaggerated politeness often seems insincere, distancing or worse so I'm skeptical of the merits of systematically overshooting like that.