When you get traffic to your directory so many more possibilities open up to you. For example, on sites like buysellads.com, when you get 100K+ pageviews per month, you may find it is easy to attract advertisers that will provide you with hundreds of dollars per month or more.
Getting enough traffic to really do something with it can be quite a challenge, but it is possible!
Assuming you have a good editorial policy and just want to get noticed more by those who are submitting to directories, you may want to look at some of the directory of directories. These sites look for quality directories and provide lists. These places can be a great place to get more traffic, but you may also get some spam submissions, so make sure you have in place some methods to prevent bots or just spammy keywords. Versions 4 and 5 of phpLD have some pretty good tools built in.
As people do start submitting to your directory, make sure you have some of the email autoresponders setup correctly. Often some of your best traffic will be the people that have already used your site. So after they submit a link for example, make sure you are setup to send them an email with more information about your site including some links of interest.
Now having only a directory of links with no compelling content is probably going to be a difficult journey, so you are going to need some compelling content. Often just like Facebook you can reshare images or articles of interest (though consider copyrights). Look at some of the popular content being disseminated across facebook and the web and then add some of this same content to your directory!
For example, create categories dedicated to humor or kittens or bloopers or TV clips. There is so much you can place in a directory, and you can reach a point where you have people combing through your directory for cool stuff, making lots of impressions, and helping propel you to a point where it is easy to sell advertising and where more people are willing to pay to submit to your site. Also see Marketing Content in Your Directory.
So hopefully you will start thinking about traffic, and soon that traffic will provide a wonderful return for you!