As a blogger myself, I often ask myself that question. And especially when running a financial blog, there is one thing that I believe is critical in establishing a long-lasting following.
In addition to high quality content, offer something new.
By this, what I really mean is write about your personal experiences, and actually make it interesting. One of the things that I believe has made this MMM blog so fucking well-read is how the dude incorporates his own life into his blog posts and then relates those experiences to the concept that he is writing about. For example, MMM wrote a blog post making fun of the doomsday'ers, basically arguing that things aren't all going to shit as they would claim. In fact, everything is fucking awesome. But, he started off his post with a discussion about his nail gun that he uses to build houses, and then related that nail gun to the fact that things really are great around here. People aren't all going to just die off tomorrow. The nuclear holocaust isn't right around the corner. Things are okay.
It's both personal AND interesting. If you can combine those two qualities, along with an ability to write fairly well, then I believe you are setting yourself up to run a very successful blog.