I agree that blogging could be a great way to demonstrate the expertise of library staff...but only if patrons can find and read the blog!

One library blog I keep in my reader comes from the Santa Fe Public Library (http://santafelibrary.blogspot.com/)...this isn't my home library, but the POV of the blog is friendly, cheerful, and informative and I read it as an example of how libraries can communicate well with their patrons. In addition, I can definitely see how this blog would be a community resource, with posts on current events in Santa Fe, updates on the library's building projects, and reading recommendations.
However, even this blog isn't doing everything you're suggesting, in part because it seems to be the responsibility of a single person, rather than the entire reference staff.
I think there are pros and cons to this approach, especially from an organizational perspective--a single poster may be the best use of resources as a library begins to blog; also, giving responsibility to one or two people with the ability and passion for the project may make it more likely to succeed. On the other hand, drawing the entire staff in to a project like this might be important for creating group ownership and, if done well, would definitely show the breadth of resources available through the library!