As a promotional tool a blog tour takes a lot of time and effort without any way to know if you're reaching new readers. I'm just finishing my first blog tour and had a great turnout on some of the stops, an okay turn out on some, but I also had a couple where I only had two people comment. That doesn't mean people aren't stopping by and checking out the posts, they just may not choose to comment but without knowing the page views for that given day, it's hard to know if you're getting the reach you were hoping for.
While I guest blogged at a number of different blogs when my first book came out, it wasn't anything organized like a tour (a set number of stops within a set time frame). While there was no way of knowing if I was reaching potential readers, I enjoyed this form of promotion more. I didn't feel the pressure to write a large number of blog posts within a short time frame and was able to enjoy the experience more.
While my current blog tour has been fun, I have to admit I'm looking forward to when it's over. I'm not sure I would do another for future books. I liked being able to spread out my visits to other blogs over a longer time frame.