I would throw this out for debate - One of the sites I have was hit by the new algo from G, I lost rankings for virtualy every keyword that I was on page on for. Just one thing seems to have remained stable and that is the page with a video on it that is related to the keyword. That is still sitting in position three page one on G (I have the top two positions with a different website). Its strange that Google has dropped the site off the radar completely for many keywords but the video page is still maintaining its position, this is not in video search its in regular search, Google returns the page with a thumbnail image of the video. It could be worth experimenting making some videos and inserting them on the pages that have been dropped in SERPS, then back link to the videos with the usual structure. Could pull your sites back, G loves videos.