What is the major reason that makes you buy links on a directory? Mine is probaly the PR or if the average heavy amount of hits per day.
Getting backlinks in a fast way, saving a lot of time, while you improve the site which is the real work you have to do.
Just curiousity, how well will like a PR5 help your PR. I mean a directory has a lot of links on each page so I wouldn't think it would improve that much.
It will help a llitle, if you are in a lot of directorys then little by litle is enough to help your PR. You may get residual traffic. But the important thing is to be in a lot of them