No self-respecting accountant spends time and effort on anything unless it adds value. The same applies to blogging. One way you can assess effectiveness is through site stat analysis. If you go to the bottom of this blog page you'll find a section in the right hand sidebar called Site Tracking, which has a series of little graphic objects. Each of these links to a stat tool. There are many tools out there to assist you, most of which are free and my selection is one of many possible sets you could apply.
By regularly analysing traffic and reviewing what people are reading, you'll soon figure out what kind of content works and what doesn't. This is crucial to retaining your site's appeal so that you become a trusted resource. And that's what your site should be about, isn't it?