I know there are probably a lot of people reading this thread who got the "thanks, but no thanks" letter who are more than a little disappointed. I can empathize with you because I had the same experience two years ago.
I'm sure you've read SS isnt everything!
Not to take anything away from those who were accepted, but I would personally err more on the side of "SS isn't anything
." Don't get me wrong: it is a great opportunity, and many of my cadet friends have some great memories of their experience at SS. I would have totally done it if I had been accepted. But will it help you get an appointment? Probably not. It might give you an interesting talking point in your ALO/MOC interviews, but it probably won't add any points to your application.
So here's the takeaway:
If you got in, awesome! Congratulations, and definitely go enjoy your time at USAFA! It is a unique opportunity and you will learn a lot.
If you didn't, don't worry about it. Honestly, it really doesn't matter that much as far as your admission chances are concerned. Focus on making the rest of your application shine as brightly as you can. This, not Summer Seminar, is ultimately what will carry you far next year.
Good luck to all.