+1 for Chris!

Sorry I just got to this question, but Nick, as Chris said, there's much more value than the initial link you get. Granted that some opportunities are really only worthwhile for that specific link, most opportunities for broken links should be turned into something far greater - a relationship.

Also, when you find URLs of broken resources, go to Open Site Explorer and plug those URLs in. Find other people linking to that same broken resource, and reach out to them as well. Ideally you should start an excel spreadsheet of different pages linking to broken resources, so as you come across more broken links, you can add even more prospects. In the end, you should never run out of sites to do some BLB on.

Hope this helps Nick!