I've been kind of curious about this, too, as I know a lot of people do guest bloggers, but I'm usually not interested in reading guest blogger posts. I read the blog because I like the original writer (s), not because of guest bloggers who I usually don't know.
I love guest blogging and having guest bloggers at my blog. My primary reason for this? Exposure, of course. I like some of the lesser-known bloggers, who are amazing, witty, and just overall great. A lot of them have very interesting reviews to read, but not many followers. If I can help them, or they can help me, by guest posting and promoting our blogs, then it's win-win for both of us!
I mean, sure, there are people who aren't interested in reading guest blog posts. But then there are those few who DO read the posts - you could gain a follower or friend from those who do chose to read. I mean, I think it's a great way to find blogs you've never heard of before aside from joining Hops and memes. I found one of my bestest blogging buddies from a guest post, and I'm happy I did.
I think it'd be good for your blog, as long as you don't overload your blog with ONLY guest posts.