I would say that depends on the keyword and on the directory site itself.You'd be surprised how much traffic some of these directories can actually bring in.
Yeah of course, as an example, I have a website listed on theporndude and a couple other directories and they bring me a couple millions of ref traffic every month.I would say that depends on the keyword and on the directory site itself.
I believe if such action is free of charge or not really expensive that is worth to add site.