In terms of longevity of genres, sci-fi fandom is one of the longest lasting mega-fandoms in existance. While individual fandoms come and go, the sci-fi genre megafandom has been in existance since the 1930s and has produced a number of well recognized, if not necessarily accepted, individual fandoms. Everyone about knows Trekkies (or Trekkers), and a cursory knowledge of Star Wars is common even among those who don't consider themselves fans of the genre, much less the movies.
A huge Star Wars collection. Even though the producers make fun of the collectors, they still cater to them, you notice.

But what are the hierarchies among these fans? And why does it matter what they are? In the first question, I'm not asking about hierarchies specific to one fandom, or the perceived 'ranking' of fandoms, but general ones between producing fans, consuming fans, and lurkers. As for why it matters, one of the most enduring images of the fan is the Star Trek nerd who still lives in his mother's basement and dresses like a character, speaking only Klingon. Or else you hear about the Star Wars fan with a huge collection of action figures. You never hear about the producers and lurkers, leading to the perception that all fans are socially inept leeches, contributing nothing to society or even their culture while wasting money. Even though the industry caters to them, they are made fun of incessantly.
Alien Culture, a sci-fi fanzine from 1949.

But you don't usually hear of the producing fans. The fans who write stories about their fandoms, or who make fanart, or fanvids. Yet these fans have been with the genre since it began. Fanzines began in the sci-fi fandom, both genre and media, albiet at different times. These fans existed before the consuming fans that most people think of came into being and up into the sixties fanfiction was even considered a legitimate part of the industry. Sometimes authors would explicitly solicit fans for their input for their universes. In fact, many of the novels written for movie and television series tend to be authored by people who began their writing careers as fanfiction writers.

Despite the origins in fandom of a number of authors, including Hugo winners, there is a disregard of fandom as an end in itself. Fandom is viewed as an acceptable stepping stone to professional writing, but not an acceptable stopping point. If you are an author of publishable quality fanworks then you are, in the veiw of a great many people, wasting your time on 'light extemporanea'. You should be publishing original fiction and not playing in someone else's sandbox.
Within the fandoms I have encountered, there tends to be a snobbishness associated with being both a producing or a consuming fan, usually focused on the other group. From the producing fan point-of-view, a consuming fan contributes little to the fandom in terms of lasting impact or effort and mistakes a physical object received as a lasting impact. From the consuming fan's point of view, a producing fan may be necessary for some of the fan memorabilia, but spends far too much time on their hobby for no return, not even the return of an object. While there is overlap between the two categories, there isn't as much as one might think.
The lurker above from Nethack. These stealthy monsters are very similar to the lurker in that they are usually never seen without something special.

And then there are the lurkers. The lurker shares characteristics of both producing and consuming fans. The lurker may buy some materials, but not as many as the consuming fan, and may dabble in fiction, but usually never shares it. The lurkers may view themselves as the highest form of fan because they aren't as 'obsessive' as the other two categories of fan. Whether they are or not, is up for debate, but that is how they see it.

Please note, these are not the only methods of categorizing fans. A broader envelope is the 'casual' versus the 'hardcore' fan, as seen on this wikipage.