The Internet is about give and take. It is not a one way street. Why would somebody prevent search engines to follow links to other sites? Are we all that selfish? Are we really scared that Google might take away some of our mystic Page Rank?
So give back something of your “link power” and don’t use rel=”nofollow”.
For those of you who don’t know what I am talking about read the discussion on wikimedia.org.
WordPress has the nasty habit to use the “nofollow'” attribute by default. The plugin “Do Follow” will help you to overcome this malaise. Just upload and activate, done!
You can always use general filters for comment spam like “WP Spamfree“. Those and a little bit of handwork should be enough to handle all kind of link spam.