I think a blog is a hugely rewarding experience, and not because of the people who read it, or because of the potential business you can generate from it.
If you're writing a blog, you have to think about what you're writing, and try to convey those thoughts in such a way that they're useful both to you and your potential audience. It doesn't matter if no one reads the blog; the point is that you have thought about an issue, and have an understanding of it. Over time, you become more well-versed in your business, because you have taken the time to think about issues that face business owners and clients alike.
You don't have to write daily. I do, but I write short articles that could easily have been larger, weekly articles. As much as anything else, it's a lifestyle choice, because I can more easily handle the shorter posts, and I think potential readers want to spend two minutes or so reading, and then move on. If you write to a more serious audience, feel free to write weekly or twice a week, and write longer articles. Whatever you do, write regularly, and people will eventually establish a habit of returning to read what you have to say. Their attention will become a very valuable asset.