I'm currently doing ONLINE versions of this and can vouch for this method. Think of niches that have people just waiting to throw cash at you. That's all I'm going to say.
In my opinion, CorrectAD may be spending a tad too much time on one directory. All you need is one advertiser onboard then you can open the local yellowpages and send a quick letter telling them that "Hey, your competition is getting a leg up on you, here's how. And here's a similar directory we have that can put you in the same spotlight"
Once you start getting advertisers, you'll get more and more. Why? How many times have you opened the paper and saw some competitors ads and thought, "Hell, they are doing it, I should too!"
I'd rather sell 500 $500 packages via 100 directories then having just one really popular one making $1000 a premium package. Just saying.
+rep. Solid post.