I do have comments disabled on 9 of my 10 blogs, but that is because I am using WordPress primarily as a CMS platform.
However, the one site where I do have comments enabled gets far more traffic than the other sites and I have never done anything special to promote any of the blogs. I think the comments encourage repeat visits, plus it adds content, which the spiders love.
I am in the process of converting my main business site to WordPress and I do plan to enable comments on the articles in the site.
I do find that 95+% of the comments are spam, especially as the site becomes popular, but Akismet filters out most and I report the rest as spam. When you find spam that Akismet is not catching, do not delete it. Click the spam link to report it as spam.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin