I don't think it will make you a better programmer, except perhaps in that it helps with practising communication skills.
However, it can be a useful way of documenting things that you've done, if only for your own benefit. It may also open up opportunities. If your blog establishes you as somebody who knows what they're talking about there may potentially be job offers or consulting opportunities as a result.
I've had a blog for about 4 years, although it's not always frequently updated. I initially started it to have somewhere to provide details of a couple of open soure projects I was working on. I also wrote a few opinionated articles but not so much recently. Most recently I just announce new releases of my projects and document things I've done in case somebody (usually me in 6 months time) needs to do the same thing.
I've had a couple of enquiries about consulting work as a result of things I've written, but nothing that I've actually ended up getting involved in.