Remember to: You should be a member of JrROTC, CAP, Scouts, Band, Chess, Spanish, Football, Soccer, Class government, or anything else........ BECAUSE YOU WANT TO!!! If you are taking any class, EC, sport, etc... specifically as fodder to help your academy application or college application, then I believe your priorities are mixed up.
If you participate in activities that you really enjoy, you will naturally do better in those activities than those that you're doing just to impress a review board.
I am not saying that the OP or ANY of the posters on this subject involved with these activities are or are not involved with them strictly for college application or because they truly have a passion for it. That's not my/our business or concern. Only you need to know. But as others have said, the academy and colleges want to see leadership and long term involvement/commitment. In other words, I'll give more value to an individual who has been in band for 4-5 years and worked their way up to drum major, than I will to an individual who has been involved in CAP, JrROTC, etc... for the last 2 years with very little leadership accomplishments.
The original question was: "Does JrROTC help"? It depends what you DO with/in JrROTC. It doesn't help at all if it's just one of many activities you've been involved in just to look good. Colleges and the academies can tell by the number of years involved and positions help, whether you are doing it because you like it or not.
I think the underlying question; that no one wants to really ask, is: "Do you get MORE POINTS for having JrROTC, CAP, Scouts, etc... than OTHER activities". The answer is: "Your points aren't because of the activity you're doing, but rather YOUR INVOLVEMENT in the activity".