I really like this distinction; it jibes with advice I've given would-be bloggers before. When you write a blog, you should have an audience. It's ok if you end up writing about yourself, but you should envision writing for the audience (mine was, initially, my mom---later expanded ;). It meant that, when I was regularly updating my blog at least, I had a readership in the several dozens. The difference between what you call "narcissistic" blogging and my idea of blogging "for mom" is the difference between "I'm writing about me because everyone should be interested in me" and "I'm writing things about me that an audience, however small (hi mom), would want to hear." It does make a difference.
In contrast, one can appear on the surface to be an altruistic blogger---writing about things rather than yourself---but still fall into the trap of narcissism, in this case, saying things about your topic because they pop into your head rather than because you think they'll aid your audience.
In contrast, one can appear on the surface to be an altruistic blogger---writing about things rather than yourself---but still fall into the trap of narcissism, in this case, saying things about your topic because they pop into your head rather than because you think they'll aid your audience.