Here's some random thoughts, in no particular order.
Proficiency with firearms is a martial art just like Isshinryu Karate or Tae Kwan Do or Kenpo or Tai Chi, and can gives a sense of accomplishment and competence just like any other human discipline. The Japanese concept of bushido applies just as much to the gun culture as to other martial arts cultures. FWIW, I have some moderate experience in the Asian martial arts culture (I was a student of Isshinryu for a year), and there are a lot of similarities between the gun culture and the traditional martial arts culture, and just as with empty-hand martial arts, proficiency in self-defense is a symbiotic benefit that is a worthwhile purpose in its own right. You may find this article interesting:
Guns and Martial Arts (from
www.a-human-right.com) (article link no longer working --bE)
Just as with the other martial arts, a lot of gun enthusiasts view training and skill development as an end in itself. A Zen thing, if you will. (BTW, to shoot well you must view shooting in a very Zen-like way; breath control, minimization of muscle tremors, concentration, sharp focus on the front sight, smoothness...) A lot of the shooters I know also have a thing for archery, which is pretty much the same thing. And my wife is into SCA fencing...
Some people pride themself on how well they can smack a small white ball with a stick on a golf course. Others pride themselves on how accurately they can shoot a firearm.
Also, I am a certifiable physics geek, and there are very few inexpensive hobbies that are more physics-intensive than rifle shooting. (Aviation is more physics-intensive, but it's not inexpensive...) Many shooters are mechanically inclined, and I'll bet the percentage of photographers among shooters is higher than in the population at large. My younger sister is a shooter and she also happens to be a professional engineer (she double-majored in Engineering and Mathematics at NC State).
Gun owners also tend to lean individualist rather than collectivist, and have a high view of individual rights. If you hang around the High Road much, you'll find nearly as much disdain for free-speech restrictions and 4th-amendment violations as for the latest gun-grab attempt, and you'll find a lot of sympathy with the ACLU except for their dyslexic view of the Second Amendment (in our opinion, though I know you would probably disagree). Note that individualist does NOT mean conservative; Big Brother communitarian conservatives are as antithetical to the individualist/libertarian mindset as any Big Brother communitarian liberals...
So I suppose it's also a freedom thing. The guns in my gun safe are a tangible reminder that my wife and I are free people. We don't own those at the dispensation of some elite individual; we can own them because we are free people. That's probably a cultural thing and I wouldn't expect you to feel the same way, but the freedom issue runs very, very deeply with most gun enthusiasts.