Sioux... from my POV HNM and/or endgame shells are about accomplishing the crazy stuff that you couldn't possibly do on your own. (this being the all-emcompassing you) Nobody can solo Tiamat... nobody can solo Kirin... but most of us want to see them... That's why *I* joined an endgame shell. It's all about teamwork, accomplishment, and friendship. Like Alauce said, sure, some of it is about popularity. If you have a bad rep on the server, you're not going to be accepted into high-demand shells. Additionally, if you know people in the shell, they will be able to step up and voice their opinions of how you play. I have to disagree with one point, though... I can only speak from the view of Aurora, but I know that skill and talent are pretty much required.
Knowing what little I know of you from our brief talks, I think you might enjoy the endgame experience. The best way to make a decision, though, is to talk to the people that you know in the shell after you've considered everything on the forums. You'll want an honest opinion from a friendly POV. Namfoodle really influenced my decision to apply to Aurora, for instance, because he told me flat-out what they did, how they did it, and most importantly, what they didn't do. I also had wonderful talks with Lunarians, AD, and IRON members about how their shells work and what they expect. Unfortunately they didn't really line up with what I wanted to do at endgame, but that's how it goes. It's kind of like sorority rush LOL.
NOTE: THIS IS A DISCLAIMER... I am ill while writing this so if anyone got offended know it wasn't intended. I know members of most of the NA and some of the JP HNM/endgame shells on our server and I respect them, so. There you have it.