You can never go wrong by learning more about music, learning basic theory will only help you to understand more about what you already know how to do, and probaly show you alot of possibilities. Whats a better use of time? learning how to construct chords or memorizing one of those books with 10,000 chords in it? Theory won't put you in a box, and there are no rules to music, theory just gives a name and an explanation to concepts, and reading music has nothing to do with learning theory. Are your songs any good? Do they sound good? Then they are good and they probaly all are written inside the realm of Western music theory, or you wouldn't think they sounded good, don't be afraid of the Theory Monster, he won't change you into a classical musican, he can be your friend