Would you like an answer that is real, tested, and not just an opinion? I'd be happy to provide that for you.
My coworker and I ran an experiment on a website that we designed for a client. They have absolutely no SEO, no on-page optimization...nothing.
We wanted to test the effectiveness of directory submissions, so we used this site and to be sure it wasn't ranking, we ran a report on the site before submitting the directories. Nothing was ranking.
We had 50 directories submitted with variations in the content to make it natural. These are the results: