I agree with cludwig that it isn't worth studying at university if you won't work in the trade, but I don't think this was what the OP intended. There are many advantages to studying music, just as a hobby. You don't have to be able to fully analyse music, of course - I can't - but I do enjoy reading analyses of music as I play or listen, whether they be at the back of a book of piano scores, or in those booklets provided with CDs.
I agree that some life skills can be learnt through music, though that isn't necessarily the case - I didn't learn a lot of teamwork through my cooperation with Bach and Chopin, haha. Joking aside, I think the primary benefit that music has given me, from a utilitarian perspective, is the reduced stress. For whatever reason, many pieces, the Liszt B minor in particular, does it for me.
Music gives teenagers something very different to what other subjects have to offer. It teaches you to appreciate to something that you may not like, or even hate! It makes you listen to things which are under the surface and pay attention to them which is a really useful life skill. Music allows creativity and helps people develop confidence. I think music teaches many important life skills which can be applied in nearly all careers and situations in life.
Music is so important in the modern world - not simply for the reason that it's of cultural importance in many places, and can bring people together because of their love for it. Yes, there are many studies that show that people who have studied music give you discipline and analytical skills better than others and improve in literacy and mathematics and team work, but there are also many personal qualities and uses for music. For me, music is something I do when I'm upset, when I'm stressed, when I want to relax etc - it's an emotional art and a way that you can express yourself. You learn about so much when studying music, like influences from other music or how to analyse really in depth. Many people disregard the importance of music in a life, because they don't realise how useful it can be for the future. Playing in orchestras and ensembles have yes, taught me how to be a team worker, but they have also taught me how to be a leader and a good role model. You learn how people work, how they respond, and how to teach and guide in a positive manner.
I think that music is a very logical subject and so can help with subjects like maths and music can help relieve stress too. However I don't think you should have to learn it for A-Levels or above if you don't want it as a career as it can be a very expensive subject to run. I think it should be taught at GCSE to the people who didn't choose it, but should only be run as a smaller course without exams so it doesn't take up as much time and is simply there to expand people's creativity and give them a break from the rest of their subjects.
Studying music will give you skills in analysis, interpersonal relations, teamwork, learning, understanding abstract ideas, connecting historical events casually, among many other skills. A musician will be able to move into many career paths because there are many skills honed in the study of music that are valuable to a large number of careers: teaching; marketing; human resources; public relations; retail; finance; etc. Music is not just music.
Music can help you with other career paths, as well as help you with general life skills. Studies have shown that it helps children with reading, mathematics and life skills such as team work, discipline, analytical skills etc. However, if you do not like the subject, other subjects and activities maybe be able to give you the same benefit, and not all employers recognize the benefits of studying music and taking part in ensembles.
While I believe music literacy should be taught to all Elementary and Secondary students, it seems a waste to study music for 4 or more years at the University Level yet not work in that discipline. I am very fortunate to make my living solely in the world of classical music as a professional musician. If I was not able to work in my field, I believe that my 8 years of formal University studies in Music would have been a waste of my time and money.