I went to a school that specialized in music, and I definitely agree that music theory helps. Also, if you can't read score or transpose, LEARN THEM. Another essential thing everyone needs to get down early are intervals; for example, diminished 4th, perfect 4th, augmented 4th. I'm one of those people who puts little emphasis on scales and such. Whilst learning scales is a useful thing, it's not required to be able to write decent music and it's way too easy to overuse them and turn your music into an unlistenable [bleep]fest. I also think that complex time signatures are BS. You don't need to get any more complex than 5/4.