I'd say Twilight fangirls obsess over Cullen more because they become infatuated with him as an "ideal" boyfriend rather than simply because he's a main character or a vampire. The whole vampire angle is really just there to increase his "perfection" -- make him eternally young, supernaturally good-looking, and inhumanly powerful. The reason I used him as a comparison point is that I've often found the slavish devotion to Boba to be based on similar elements -- as you note, Boba looks extremely cool and is considered a badass. He's an idealized character that is pure and utter wish fulfillment for fans (as Edward is for fangirls) -- they all want to look as cool as Boba, be the best bounty hunters in the galaxy, take crap from no one, and be able to talk back to Vader when no one else can. Just as a lot of girls who read Twilight put themselves in Bella's shoes to pretend they have an immortal, impossibly handsome boyfriend who is constantly tested to extremes by their presence because of his intense desire for them, but holds out due to "love." The details are different, but the mentality behind it is largely the same. Personally, I'm not interested in such characters. Tony Stark is another really popular example, if that's a comparison you'd prefer to Edward. As are a lot of video game characters. They exist for us to play out our fantasies, but I find that robs them of what makes them flawed, three-dimension characters.