I think the Dunbar Number may be a useful tool for thinking in broad terms about why society is the way it is, but using it for more personal stuff strikes me as a recipe for disaster.

In the latter case the more interesting question is how many people in those traveller's monkeyspheres reciprocally hold the traveller as a social intimate?
Yeah, that's a damn good question. We all know situations where people are close to others who don't hold them in the same regard.