I find zircon and wolf pack to be the best writers on the forum, myself.
On the issue of style vs substance -- there is no dichotomy, as it should really be substance and style mutually reinforcing one another. If one is perpetually chosen over the other, you will likely end up stunting both.
Clear writing contributes to clear thinking. The greatest winner of all when you write a concise and cogent post is not necessarily the audience -- it's yourself. There is a lot of evidence that the potential of human reason, in the absence of writing, is actually fairly limited. It's the codification of ideas, and of thought, that allows deeper, broader, and more complex thoughts. With writing, people can develop complex and interesting stories such as The Dark Knight, multiples ones throughout their lives. In mathematics, there is an emphasis placed on the proper use of symbols to communicate.
I started putting more effort into my writing early in college. I realized I wasn't as good as I believed myself to be, so I focused on going over my writing, rethinking my ideas. Circling back to the first point, the best thinkers are not those who are constantly criticizing others, but rather those who constantly self-critique, who ask themselves if they're really sure about what they're saying, who review and adjust their words accordingly.
For whatever it's worth, I think you have a clear "voice", which is the most important thing. I also find you easy to read.