As a different perspective....
In my DS BCT this summer, the kid in his squadron who got Outstanding cadet for BCT was a CAP kid who knew drill, shoe polishing and overall was a great kid according to my son. I assume JROTC could give you a boost like that in BCT.
Maybe an ALO could give you a perspective, but I don't know that admissions cares whether you do JROTC vs CAP vs Football vs Debate. I don't know that they weight activities. I do know they examine your level of involvement, your effort and dedication in that extracurricular - along with your ability to demonstrate and communicate that during the process. If JROTC interests you, then by all means, go for it. If you were only going to do it to try boost your chances of admission, I would encourage you to find something else. Find an extracurricular that you can be passionate about. Something that interests you. Something that will expand your horizons or expose you to something new or even something that will put you out of your comfort zone.
I know this board is all about the academies. But, you also have to think about your life. Doing things just to get into an Academy is a short term view. If you grind out out JROTC just to pad out your resume, you may be missing opportunities to explore other interests. And, again, I'm no ALO, but I am willing to bet that a kid who pursues a non-JROTC extracurricular with passion and is dedicated and committed to it, will be a more interesting and impressive person that the kid who did JROTC just to pad the resume.
And another thing, my DS knew nothing about polishing shoes, marching, making beds etc at the start of BCT. But he listened to his prior enlisted roommate and came up the curve really quick. Honestly, that kind of stuff seems super important in BCT because thats a LOT of BCT. Anyone can pick up those things fairly quickly and close the gap between them and a JROTC or CAP kid really quick. I pass on to you the same advice I gave my DS, pursue and develop your interests and the resume will take care of itself. Finding, developing and pursuing your passions will make you a better candidate AND a better you too.