I was born the year trek started, so it was off the air before I really even became self-aware. I watched Trek on my living room TV with my dad when I was about 5. However, it really wasn't until Star Wars hit in '77 that I fell in love with science, space and space dramas. Those were the years that things really got into the Zone; from '76 to the early 80s, we had Star Wars, Trek the Movie, Battlestar Galactica, Aliens, and Close Encounters. Not to mention that the whole UFO and UFO abduction thing was really hot too. It all got me thinking, and more specifically, it got me thinking about what's out 'there,' and how we will live in the future. I gobbled up books, comic books, TV and everything else that I found on the subject. Other than football, motorcycles and girls, I lived and breathed Trek and everything else associated with space during my High School years. This was before cell phones, home computers, and Cable TV. Heck, I didn't even have a VCR until I had graduated High School. So, if I wanted to see a show, I had to catch at the time the network was showing it, or I was screwed. And that was fine to me because I had a myriad of other ways to entertain myself.
Today, we have all of this access to everything, any time, any where, and there just seems to be something...soul-less about it, I guess. The new movies are absolutely awesome; great effects, sound...and the acting is good too, but at the same time, not as nice as the original Trek seemed to me in 1972, when I was a kid watching Trek on our 'BIG' 19' TV.
And I think that has much to do with nostalgia. The reason I say that is because
everything today seems less awesome to me; amusement parks, pizza, Christmas, shopping malls, TV in general...I just think we tend to think about the past in a way that leaves out the drab, the melancholy and the aggravations that existed then. Things were never as nice as we think them to be later and that may even be true for us 25 years from now when we think about today. I sometimes listen to my mom telling about how she grew up in a house without electricity, and how magical things seemed to her.
To me, Trek is less cerebral than it once was, and at the same time, it is also less fun. I can't put my finger on it because there are
many shows in TNG, DS9, VOY and ENT that are every bit as well-developed and written than those from TOS. But it just seems that way to me, and I guess that is, in part, because it's not 1972, and it never will be again. Nostalgia.
I caught my teenage daughter saying that she missed the 'good old days' (which, to her is like 2010
).
The cycle continues...
so it sounds like you're about 2 yrs older than me, at most. Your post sums up my feelings quite nicely also. I was a major TNG fan through college, and drove my friends nuts when I'd try to engage them in conversations about the themes in Trek and how they apply to our life, or current events. 
