Most media outlets track impact using a variety of tools. Media metrics tools track how many people see content, how they interact with it, who they are, how engaged they are. Surveys help you understand who is using your content and how. Clip services like Meltwater can help you understand if your content is being picked up and leading to further coverage of an issue. But generally actions taken by your most influential audience members are more difficult to track. For example, if a policymaker sees a story and wants the journalist to speak to a policy committee. Or if a community activist uses a video in a local meeting. On a good day, impacts like this are usually stored in spreadsheets, but more typically stay locked away in a journalist's inbox. The Center For Investigative Journalism's Impact Tracker is a tool for recording and tracking these kinds of "offline" impacts. This article talks more about its use in the newsroom. Unfortunately it remains a Drupal install, rather than an easy web service, which is a fairly steep barrier to entry.
Still, there aren't any great tools out there that solve this particular problem, and the team at CIR is very collaborative and open to help and discussion.