As a guitar teacher, I know that lessons multiply the potential of improvement greatly for any students. Of course, talented ones, that have a good ear, great rhythm, and talent, won't need a teacher to express themselves on the guitar. But with a teacher, they'll be able to express themselves in a lot of ways, and better.
I have been self taught and I have taken lessons quite late in my playing, and I guess I know both ways. I know I could have never reached the level I have reached without my teachers (but I wouldn't be as bizarre if I weren't self taught...)