Seems to me the only relevant question is the last one, the rest all seem pretty obvious? For some it's the journey, for others the destination (pretty much like everything else in life).
When I was a kid modeling taught me a lot about cars and how they work (also aircraft, naval craft, armor, etc) as well as building dexterity, problem solving, and building confidence. Now I build as a stress reducer (most of the time ) and to have tokens of the real cars I would own if I were Jay Leno. Sites like this one that let us share our work and constructive criticisms have helped me step up my game although I wouldn't call myself anything above average. Great thread, I hope this helps you in your studies.