Is forum presence (of which I have little), really helpful to your brand? Many people use pseudonyms when posting to forums.
I also think many people (again, like myself) are reluctant to post a blog or even a forum reply because it's natural to compare your knowledge to the collective intelligence out there. It's pretty intimidating.
I wouldn't be reluctant to post a blog or forum reply just because you don't know as much as others out there. Sometimes that post can solidify the knowledge in your mind about some problem you solved and how. Maybe it wasn't the best solution, but it worked at the time and you learned from it. Same for answering a forum post - you may present an idea that someone else didn't consider. We're often impressed or intimidated by people who are regular speakers or posters, but they often know their areas really well so are confident in those areas. I find Brent Ozar's story somewhat fascinating - someone who took some initiative to make his own path, but specializing in what he does well.
All that to say - don't be intimidated. If you have a suggestion or answer, put it out there. Worst case scenario, you'll learn some better ways to do things from those who comment on your ideas. Learn, update, move on, and keep posting. Obviously don't throw out something not even close to helpful or on-topic, but do offer your experience when you think you may have an idea.