Google hosted a special hangout with John Mueller and a colleague from the Dublin office who works on structured data and rich snippets. During the hangout, at the 43:50 minute mark, Google addressed a question about rich snippet spam not being removed even after repeated spam reports.

Google said that they do review all rich snippet spam reports, just like they do for normal spam reports. And if there is a clear violation, Google does take action. Sometimes there is not a clear violation, so no action is taken. In short, if you see rich snippet spam and you report it and nothing it taken off, then it might not be in violation.

Here is what the Googler said:

Here is the video embed:

Forum discussion at Google+.