Writing begets writing. The process of sitting down and figuring out what to say is something that gets easier and hopefully better with practice.

You're right. There isn't a shortage of mediocre content on the web. I use this method to improve my writing. Consistency is everything. Also if I have ideas to share (like this post) that may help people, I think that is worthwhile.

While I'm not sure they should always be public, I think blogs are a good way to force yourself to write. I recently started one because I want to (a) become a better writer and (b) to have a place to put personal reflections and pieces of interest. While each individual blog post might not be read-worthy, the added experience will likely help in your future documentation practices.