Eventhough I'm not working in a field related to my degree, I would still go back and do it again, because I genuinely enjoyed my subject.
You're right in that a degree in itself doesn't help you with most graduate jobs; in fact my employer has a school leavers programme alongside the graduate scheme, and the school leavers basically do the same tasks and have the same responsibilities as the graduates but for less money.
But I actually feel quite bad for the school leavers. They're stuck in the world of work from such a young age, with a lot of stress and responsibilities that I was free of at their age.
Why miss out on opportunities that you get at university that are hard to come by when you're working? I was a very shy 18 year-old with no social skills and little interests and hobbies. Going to university helped me meet people from all over the world, make new friends, try out a lot of different clubs and societies, volunteer etc. I came out a more confident person, with a better sense of who I am. I think this would have been a lot harder to achieve if I had gone straight to work. There would be fewer opportunities, more stress and less free time.
So I would still go to university for the things you listed as a negative point i.e the prolonged adolescence, because you're going to spend the rest of your life working every day, so what's the rush? Also, my passion for my subject made it worth every penny!
But each to their own I guess. If you think it's a waste of time & money, then don't go. But for people like me, it's definitely worth it!