I've been playing the guitar for five years. It'll be six this April (I got my first guitar on my thirteenth birthday.) Practically everything I've learnt about the guitar has been self-taught. When I started out, I did have two guitar theory books that I sometimes read, but other than that, no formal teaching.
Guitar lessons
might improve your playing. I think it depends on the type of sound you're going for. I've considered getting a few lessons myself, because I'm quite unimpressed with my soloing ability. Rhythmic, minimalist guitar is my specialty (think U2, Modest Mouse, certain elements of Radiohead, Echo & The Bunnymen, etc.) but I'd love to be able to crank out a giant David Gilmour solo, or something like that. I just need to get the kinks out, and think that a proper teacher might be able to help.
So yeah, if you want to try to branch out into more technically-orientated stuff, lessons might be the way to go. At least a teacher would
force you to learn the scales (I'm very bad when it comes to practising scales
) And don't limit yourself to U2 either. That's the mistake I made. The Edge is a great guitarist, yes, but if you limit yourself to that style, your skills (mine did, at least) kind of tend to deteriorate.