I agree and I think that it applies to many of Mr. King's books - the way they remain relevant and even change their meaning for you when you reread them years later. I believe that's because he is dealing with human ideas, emotions and motives and those - like it or not, are pretty much a constant.
4th-8th grade, if you asked me what my favourite book was, my answer would have been Carrie.
To be fair, in fourth grade, I had not yet read Carrie (or even seen the film), I was still working my way up to 'grown up horror'*, and still quite a bit squeamish. But I grew up in what I affectionately refer to as 'The Vampire House', with people all-too-easily dubbed 'The Addams Family', and was thereby blessed with a basic understanding of the plots of anything scary.
I could not envision a happier ending. I mean, not in real life. All too often, the idea of developing killer telekinetic powers seemed to my childhood self far more realistic than the idea of blossoming from an ugly duckling into a beautiful swan.
(I was not diagnosed with Asperger's Syndrome until I was in college and already knew some people who liked me for my crazy self. I am still not a beautiful swan-- maybe an overweight and somewhat pimply swan-- but I also haven't killed anyone with my brain, so all in all perhaps I'm breaking even.)
To this day, Carrie, has been the SK book that I have read the most amount of times. It has the most emotional resonance to me, as I feel like I was Carrie in middle school. I think if I had her powers, some kids at my school would have been fried.