One of the things that I have learned over my years of playing both acoustic and electric guitar, is that jamming with a friend or finding other guitarists/musicians to play with is one of the greatest ways to get out of the "I'm not getting any better" doldrums. I'm self taught and learned completely by ear. I played solo for many years and thought that i had hit a wall with my playing and technique. I played the same songs over and over, because I knew them, but they didnt seem to sound any better. A work associate mentioned that he played guitar and asked me to join him one evening to jam. This turned out to be a huge milestone in my musical career. He showed me some new songs and techniques that just blew my mind. Some things (bad habits) that I had been doing were holding me back. My friend, on the other hand, is an accomplished musician enjoys some of the things that I have shown to him as well. He says because I never had lessons, that my technique is raw and he really enjoys the "unstructuredness" of my playing. We have now started a band and I am learning new songs, chord positions, lead lines, etc that are easy but a challenge. I could have been playing all along. I've really started to re-learn guitar
Bottom line, work with as many musicians as you can to learn new things. The guitar is an amazing instrument and has many possibilities, many sounds. Lessons are a great thing but make sure that you learn from many instructors and dont limit yourself to any one style.