I bet a lot of people who study languages will notice that their knowledge of English grammar has improved because to learn their chosen language, you have to understand how sentance structure, spelling, rules and other grammatical features work in your own language.
Without trying to generalise, there are a lot of people who I speak to who have little knowledge of our of language. Not just literature, which is also important, but I think we should be taught more about the way our language works. Not the extremely basic things taught in fundamentals, but other grammatical things. I dunno. Widening our vocabularies, writing in different forms (no, not generic essays on literature in different forms), more debating and creative writing.
Having said all that, I think it's extremely important to have a good ability in your own language. It's all very good and well saying, "oh, you only need the basics", but I think we learn to be a lot more coherant and sophisticated through our study, for when we need to be.