CainIV - 3:26 am on Jul 25, 2012 (gmt 0)
Is there any single piece of evidence that cleaning up helps?
I don't see any direct evidence, of course this is part and parcel why Google uses so many variables and announces so many updates - to blur the line between changes and increase the difficulty of reverse engineering. Each subsequent update will likely be more complicated in nature making this process even more difficult.
I would say that cleaning up backlinks is a good idea. While doing it, be sure to take an aggregate and individual top 10 snap shot of exact match anchor text links, long tail seo anchors, brand and www anchors and do come comparative analysis.
Ensure your profile falls within those norms, to start.