A blog is absolutely an asset! And it’s a great marketing tool and lead generator, too. I am a writer with a full-time writing business, so having a blog furthers my business and acts as a sample of my writing skills.
I love blogging, and originally got into it because I loved it — long before I had a real business and services to sell. I think you’re right and it is so important to use blogging as a tool, not as a whole.