These are also things I think. But are they (developer) must think about money when they write something that had nothing related to money? For example, open source and knowledge. Whether the term “worth” you mean here is the income? My English not so good in terms.
If you have a site that displays your portfolio, a blog can improve the search engine rankings and increase the amount of traffic, possibly leading to more work. So as a developer I would consider it for sure, if you have time. I think the content would depend on your style and how you are presenting yourself. It should be more personal so people can get to know you better, yet still professional so you don’t scare people away. And should target the same market that your site does.
I have a personal blog that sits outside of my ‘developer’ persona. I have a developer blog that talks about things that I’ve found difficult and the solution that I’ve found. I love finding a blog post that answers the exact search that I’m performing. I hope that my blog can serve that purpose to others.