As has been accurately noted; going to summer seminar will not "Officially" help you get an appointment to the academy. It isn't designed to help you with your application; give you ideas how to improve your application; etc... That wouldn't be fair to the thousands and thousands of others who applied for summer seminar and want to attend the academy. It's a program designed to give the individual a better understanding of the air force academy, and a taste of what they are possibly getting into. To do anything more than that would be totally unfair to those who didn't get selected. Remember; those who got selected were so more based on location than anything. Simply trying to "Spread the wealth" among applicants. There's nothing on your SS application that is "Official". It's all self reported and the academy didn't do a lot of background checking.
Unofficially; as has been noted; people like your representative, senators, and even ALO will be interested if you "Applied, were accepted, and attended". If you DIDN'T APPLY, do you "REALLY" want to go to the academy? If you did apply and were accepted and didn't go; do you "REALLY" want to go to the academy. HOWEVER: They all understand Boy's State. ESPECIALLY your MOC's. If you say you applied to Summer Seminar, were accepted, but had to decline because you were then also "Nominated" for boy's state and had to choose between the two, and boy's state gave you more experience with leadership an government, that is totally understandable, appreciated, and accepted.
There are very few things I'd recommend turning boy's state down for. Very few. Summer seminar isn't one of them. Now; maybe the army cares more about Summer Seminar than actual leadership programs like Boy's State, but this isn't WEST POINT. This is an air force academy forum. If when you have your ALO or MOC interviews, and you work in how you were honored to have been chosen for Summer Seminar, and that you would have LOVED to have been able to spend time in the summer at the academy; but being selected for Boy's State would be of more benefit to you as an academy applicant and as an individual learning leadership and government; your ALO and MOC will totally understand that. Now; if you don't explain to them why you turned SS down, that you're own fault.