If you find the directory useful as a user then it's safe to get a link there. If you wouldn't use the directory yourself it's best to just steer clear of it. I can't imagine many situations in which you would want more than 10 niche directory links because there just aren't that many quality directories any more.
Use SEOmoz Toolbar & Google Analytics for 301 Redirect Opportunities
8/2/2012 Diluting page authority can be a major problem for ecommerce sites. SEOs all over can benefit from this quick review of how to use the SEOmoz toolbar and Google Analytics to identify 301 redirect opportunities. This approach really focuses on low hanging fruit because it takes less than 10 minutes to uncover good finds. Here is a quick guide to show how we identify 301 redirect opportunities and the results of a successful implementation.