I've been blogging six years for the mostly selfish reason of forcing myself to write on a regular basis, to work through my thought process, which results in more creative material.
My brother talked me into tweeting two years ago so he'd have one more follower on Twitter. I tweet random thoughts that don't make it into blog posts and occasional work updates.
I understand that authors, entertainers, and anyone who has wares to sell may feel forced to have an online presence, but as you say, Steve, unless used properly a blog or Twitter account can fall flat.
I would think if one has enough personality to write a book that others like, one has enough personality to blog or tweet. Many authors say they enjoy touring for the opportunity to connect with fans after sitting for months at their desks. A blog can be like a tour stop where you get to talk about stuff that interests you more than "Where do you get your ideas?"
That said, I usually don't get to know people or start reading their works from their blogs. I prefer to meet them in person and then read their blogs.
I'm a writer with a blog, but my blog isn't about my writing. It's about snippets of life that move me to blog. If you read my blog, you may see what inspires a good deal of my writing, but there are few exact matches. For me, fiction and poetry involve creation, synthesis, not simple description or transcription.
I hope that if you read my blog and we meet one day, we'll be able to recognize each other like old friends. I'm not the kind of friend who overshares in writing or in person, and for that, you're welcome.