I can only give you my personal experience (from Class of 2009). I validated 4 semesters of Spanish during Plebe Summer, which allowed me to get a Spanish minor with only 4 additional courses (also validated Chem 1). I was an Ocean Engineering major, and do not feel like my schedule was overloaded.
My decision to minor in Spanish wasn't based on any future use in the Navy. Once in the Navy (surface warfare, then lateral transfer to oceanography), I did not automatically receive a pay bump. From what I understood at the time, I would have needed to take a language proficiency test, as well as prove that I was using that language as part of my job. I did not satisfy either of those requirements, so never received any additional pay. Despite that, speaking Spanish was extremely useful in deployments to South and Central America!
My reason for pursuing the minor really came down to "why not?". I'd always been interested in becoming proficient in another language, and since it didn't overload my schedule it made sense to me to take the classes. I had a vague notion of "maybe this will open up some opportunities down the road", but it wasn't a driving factor. My Spanish courses were small, only 8-10 people in each class, and I really enjoyed them. It was a nice break to leave a tough Engineering course and do something completely different! I am no longer in the Navy, and work as a Civil Engineer in design and construction management. While I fell out of practice and don't speak fluently anymore, I know enough to understand others and get my point across when needed, which in my industry in a very valuable skill!