"How important is knowledge of music theory for the working drummer?"
"Is music theory essential to having a good career in music?"
If you are going to attend a music school to major in music, you'll notice that part of the curriculum is that you be proficient in not only your main instrument, but piano ... as well as some vocal training. At the university I attended, I had to have four semesters of piano (plus pass a proficiency test) and two semesters of voice. I also had four years of Music Theory and History. All of this was required since I was a Music Performance major. If you plan to major in Music Business, Music Education or Music Technology ... the requirements are sometimes about half that simply because you are taking other classes specific to your field of study.
In this day and age, the more well-rounded you are ... THE BETTER. Unless you are a music prodigy of some sort, you will find that you will probably need to have other irons in the fire to make your income balance out as a professional musician. By this I mean that you may HAVE to do more than just play drums — arrange, compose, teach private lessons, etc. Having a STRONG music theory background is going to be a must if you want to accel in these areas. [As a side note, if you play guitar, that is going to be like piano for you ... however I recommend that you still have some basic piano skills. This is largely due to the fact that you can visually see what's going on (theory wise) much better with the keyboard layout on the piano.]
For the working drummer, I feel that you need to have a solid knowledge of music theory. Sure, there are numerous successful drummers and percussionists out there who know very little theory and/or can't read music, but those numbers have been decreasing over the years. With all the stiff competition in the music industry, the key to success (in my opinion) is based on what you can bring to the table. If you can offer a band your knowledge of music and music theory, and not just being a great player ... you are going to be an asset to them. I can't tell you how many times I have been the one explaining/teaching a chord progression, meter, melody line, etc., to a fellow band member.
I could go on and on about this, but I think you get the point. You have EVERYTHING to gain from studying music theory and absolutely nothing to lose. If you are going to make your living in music, you need to know MUSIC. That's the difference between a musician who happens to play drums and the unfortunate drummer stereotype. The question you have to ask yourself is ... which do you want to be?
