Martin, i gave a try for the dofollow plugin, but the results was different than the expectations. People started to place keywords on their link anchor and i hated this so the dofollow must gone.
I think that there is only one thing that may improve the interaction of a given blog and it is the regularly published totally UNIQE content. For instance there are tons of webdesign and seo blogs, so you need to try to post about things that can not be found elsewhere so your blog need to be outstanding to make visitor post comment relating your thoughts. As i saw you have already found your own niche with this semantic html project
And a short update here. I think that the template you use is a keyfactor for getting comments, so need to select something fresh and youngish which encourage visitors, of course only if you are not MR. Matt Cutts, because he need nothing to receive tons of comments.