I also own a few other blogs on the topics of Stock market trading as well as a Detroit Red Wings blog. I put a little bit more effort into those blogs and am making even more money off them each month. Long story short, if you are considering making a blog to make some extra money and can write about a simple topic, do it. When I first made this blog 4 years ago, I was in high school and had no idea that it would still be around in 4 years, let alone still making me money. I am now in college and do not have nearly enough time to be constantly updating it, however when I do my earnings increase. While I am not getting rich off of it, it's a fantastic way to earn some extra money each month.
At first, creating a blog is a lot of work. You have to find the right niche, do keyword research, get backlinks, etc. However, after the beginning stages are over you will find yourself doing less and less work, while earning more and more money off of services such as Adsense (which is what I use) due to increased traffic. So if you are on the fence about whether or not to create a blog and already have an interesting niche that people would want to learn more about, then go for it! I can guarantee that your future self will be kicking you if you decide not to do it. This is corny, but....you wont succeed unless you try. Good luck and make some money online!