Boldly say NO. it will help but not sufficient. Directories are just link farms and Google may neglect those.
Good directories help if you get your link in a relevant category, it's another relavant backlink out there. Most spammy pr0 directories are a waste of time and your link will sit next to spam sites and prono sites that's called a "bad neighborhood" which a lot of people think can harm your site. And google does say they penalize people for being in "bad neighborhoods". Some PR0 directories that are new are good you can get in for free and if the owner cares for the directory it will be PR2-3 next year and be a good link but this is probably about 1% of new directories.