Maybe. If you have some time and some interest, I think so. I have about 35 of them and keep them updated by email, since it makes it pretty easy.
Some of the blogs are stand alone, but others are part of a site and they help to bring in more visitors to the site than the site does by itself.
The main thing is that you should be willing to make a comittment to post a new message at least once a week, and if possible every day.