Comments are a good indication of the popularity of your blog. Having many comments on your blog actually helps with generating more traffic, because people do rate your blog slightly by the number of other people who read your blog. Make sure you have a listing of all your recent comments at the side of your blog, it will generate more comments, and people read them. They want to know if your blog is an authority on a subject and comments is one quick way for your audience to determine your blog’s authority on a topic.
I would respond to comments by email if appropriate. You might get a lot of comment spam, either from spam bot engines for blogs or people writing comment spam. If they are just attempting to get a link and sell a product, I delete the comment, and ignore the poster. I will usually ban their ip address. However, if a comment is made that follows the tenor of a conversation; I will usually keep the comment, even if the commenter has also put a link to their site on your blog. If the comment is good and generates some additional thoughts on your part, such as a question, I would definitely post another comment on your blog maybe with a link to your earlier posting and the comment, plus a link to the other person's blog, if they have one. If the commentator has a blog, read their blog and post a comment with your link, if their content is relevant you just gained another good link.