Narcissism may have increased relative to the past, I don't know, but it seems a simpler explanation that travel has become much cheaper as time has gone on, so now there are more people capable of participating and talking about it. Couple that with the development of technological tools able to amplify communications to more people than in the past, and the incidence of travel (among many other topics) becomes more visible.
It comes as no surprise that people do things that they see other people doing, which I don't think has changed much as time goes on. So, people travel, they talk about it, more people "hear" it, and more people travel as a result.
I'm saying the presentation is a symptom of the purpose. In my opinion, social media are not designed to share ideas or experiences, but rather, as a means to seek approval from others. I think that somebody who Instagrams his trip is more likely to be doing so because he wants others to see what he's doing and judge him on it, rather than so that he can document the trip for himself.
But that's only my opinion and not a matter of objective knowledge.
It comes as no surprise that people do things that they see other people doing, which I don't think has changed much as time goes on. So, people travel, they talk about it, more people "hear" it, and more people travel as a result.