I agree, too. I find it difficult to understand that people who play an instrument don't want to understand music better. And if you do, you can't beat a good school to study at.
After I'd been playing for a few years, I decided to get serious and found a teacher who specialised in jazz and fusion, workin on improvisation a lot, and understanding the progressions you're playing over. Chordal harmony theory was covered a lot, as it's the beginnings of improvising, so I got a good grounding in that from him.
But I really wanted to understand chordal harmony more, things about progressions and such, even though I already had a start in these areas.
Technique is something that requires practice, and you can benefit a lot from having a teacher, pointing out what's going wrong, how to improve it, but you can't escape the fact that you have to go away and practice a lot on your own.
But for theory, there's no better way than to get in a class (whether at college, university, or, if you're lucky enough to live by one, a dedicated music school).
I began a degree in music at university, but unfortunately had to quit because of lack of funds. Whilst I was there, I learned a lot. Sight reading was a great skill to work on, score analysis, compositional styling, working with chromatic scales, substitutions, all of this stuff is fascinating and can be really rewarding to study. The professors were very good teachers, and you can't beat the feeling of working under people who have made it their life's work to understanding music.
As luck would have it, a new dedicated institution for music has opened up in my city (chaired by none other than Bruce Dickinson!). I'm looking into enrolling there and completeing my degree. I might be able to start this September
at least you remember your former teacher's Feanor 
