I disagree with your characterization of the Panda update. It just seems factually inaccurate to me. I never heard from any credible source that “what they did was to manually categorize thousands of content farms and devalue the link juice of the backlinks coming from many of these websites”. The fact is that many articles on those very websites continue to rank very highly in SERPs.
From what I have learned about the Panda series of updates is that Google, for the first time, has begun to assign a quality score to pages within their index. Google spokesmen and engineers have publicly warned webmasters for several years about quality issues and originality of the content on websites. After working on algorithms that check for quality issues in the content they finally began rolling them out this year as the Panda updates.
The Panda series of updates seems to act like a weighting factor that lowers the relevancy scores of each page with low-quality content. It also seems to lower the value of outbound links from low-quality pages. So if you have a website, that has a lot of pages with low-quality content, the link juice that passed through your internal links have been devalued. Similarly, if you were receiving a lot of link juice from backlinks on pages that contain low-quality content, that backlink juice is now reduced.
If you have pages that contain low-quality content, or you rely on link juice from pages with low-quality content the Panda Update had an effect on your rankings. I have seen no evidence that the Panda Updates targeted specific websites, just specific content with low-quality levels. If Panda effected an entire website, then the entire website was relying on low-quality content before the update.
Also, whether the content is spun, or not, doesn’t seem a cause. With rare exceptions, there is no such thing as no spun content. Virtually all content is spun, either by software or the creator’s brain. If the spun content is high quality it remains unaffected by Panda. If the content is low quality, regardless of the use of spinning software program in the creation, or not, Panda will impact it.
It seems to me that many folks are failing to understand exactly what Google considers quality content. Generally speaking, quality means being free from defects. Poor grammar, bad spelling, excessive use of passive voice, poor layout choices, and similar content issues all seem to act as triggers for low-quality scoring in the Panda update. Yet we rarely see threads here on this forum that discuss Panda in this context. Why do so many people seem to not get it?