Relevance is the most important factor in any search engine algorithm. A link from relevant directory is much more valued than from a general directory. For e.g. if you have a site related to law, the link from a Legal Niche directory is much more valued than a link from a general directory. It is quintessential for any website to be listed in the niche to rank good in the search engines. This not only offers SEO advantage, but also sends targeted traffic to your site.