It seems that rules of courtesy are intended to bridge this gap. The problem is that, unlike many other rules (laws and morals), rules of courtesy are very hard to justify and vary quite widely. For example, it seems that people of my generation consider spitting in public basically rude, but excusable, while people of the generation after mine consider spitting in public basically permissible. (From the perspective of courtesy, that is; putting aside prudence and public health and such.) It's not at all clear to me how one would argue for either rule.
So, if courtesy is supposed to help us out with these superficial relationships, it's a very poor, crude tool. Which suggests to me that it should be abandoned; but this then leads back to the original problem: what do we owe to people to whom we seem to have more than a duty of non-interference, but less than the special duties attached to closer and deeper personal relationships?