Low search keywords that don't show in googles keyword tool, how to tell if they're good?

Aside from running googles keyword tool and PPC campaigns, are there any other ways to tell if a keyword is worth targeting?

I'm a niche that naturally gets low traffic, but provides a very high ROI.

The niche is mold removal/mold remediation.

For instance, "mold remediation nj" gets around 480 exact searches a month. "Mold remediation new jersey" gets around 140.

But I'm trying to figure out what towns or counties I should be targeting.

Like right now, I'm trying to figure out if its smart to target "mold remediation monmouth county nj".

I analyzed the first site that showed up, it has about 77 backlinks, and a small % are paid directory links. Which made me think "why would someone be paying that much for directory links if this keyword wasn't worth targeting?"

The potential profit for 1 sale in this industry, is a few grand. Like most home improvement niches.

I also know when I search for services, I rarely tend to put just the state, but the county or town I'm in. I've never used SPYFU before but I hear it can spy on competitors PPC campaigns. Is there anyway I can use this to tell if certain keywords are good?

Should I just assume because people are competing/spending money on keyword, that its worth targeting?

The real issue is, I've made up a bunch of pages for various towns and counties, but am not sure which ones to focus on. It doesn't seem like a smart idea to build backlinks for all of them, considering how much work & time that would take. I can either do backlinks really slowly, for all of them, or focus on a few more aggressively. But then the obvious question becomes which ones? And that seems to be really difficult to figure out.

Thanks - Red