lammert - 2:09 am on Jul 23, 2010 (gmt 0)
The PR value displayed as a green bar in your browser is not in all cases an indicator of the value which Google and other search engines give to that page. There may well be link juice flowing from the page to the linked destination.
Another reason why a link still may have value is that human visitors may use it to find and visit your site. Directory users are often highly targeted visitors and a directory link could therefore well be worth the money, even if there is not much value in terms of search engine rankings.