I heard that one of the best ways to increase comments and visitor relations are do-follow comment sections on your blog. If you have one or like to SEO your head away post them here.
My blog is DoFollow, but it attracts a lot of "worthless" comments by people just trying to get free links (and it's usually quite obvious).. i always delete the spam/worthless comments..
Yes, its just a way to get worthless comments, moreover, ones who want to comment would never check whether the link i nofollow or not. A better idea would be to make use of better comment templates. Template is never small issue. Make the template such that it is not a comment, but it is a discussion section of the page. More over, I have this idea all the time... Make a chat section for your visitors for whole website. But the key here you create a chat post, the chat messages posted will be comments of this post. This gives a feel as chat box. And if the user wants to view the complete page, he should be able to view it with the link above the chat box.
Personally I pay no attention to dofollow or nofollow on blogs, because I'm not looking to comment on "linkdumps". Most of the people intentionally seeking out dofollow blogs don't really get that traffic is about TARGETING your visitors not dumping a bunch of links to try and rank for SEO. So set your blog to dofollow and you invite clueless people to dump stupid "Nice post" "Good job" comments that do not contribute in any way to the quality of your site.
Dofollow has both advantage and disadvantage. Dofollow blog can get more comment but most of them are spamming, you might need to spend some time to delete those spam comment.
Good DoFollow blog will still moderate the comment - don't concentrate you attention on this. Just comment on authority blogs in your Niche and it will help you rank as Google actually follows the link now and pretty much ignores its onw nofollow attribute.
My have plug-ins Top Commentators, Do Follow, KeywordLuv and CommentLuv to encourage you to leave quality comments.