How can I be more than mediocre on the guitar and piano?

Okay, well I've been playing guitar for a few years, and I'm afraid that I'm not that good, I have always picked up on things very easily, first year of beginning band, I learned so fast and I was so natural at the Clarinet that within five months of being in beginning band I was placed in intermediate band, and got first chair. But than I began to teach myself piano, and I'm not very good, I've always wanted to fly across the keys like Beethoven, but I can only play the treble clef half, I cant play both treble and b parts of the song. Also I learned to play guitar faster than everybody in my group, but somehow I can't help but feel like I suck, because I have not grown since my guitar cl, because my teacher moved to Israel, and I don't know how to teach myself, and so I'm frozen at being the really good, but beginning player. I also picked up on Opera well, which was my mother's idea. And I've all of a sudden took up an odd interest in the Cello. I don't want to come off to pretentious. And I'm terribly sorry that I'm blabbering on.