I'm convinced of this myself due to my 301'ing experiments. The two most popular pages on my worst Pandalized site showed little increase after I moved them. It was only after I reworded them from top to bottom that they made a significant recovery.
The reason they were still the top drawing pages on the Pandalized site was that they were the top drawing pages before Panda hit. They have the largest numbers of incoming organic links, and were #1 in Google for some significant two word phrases. This drew a huge amount of copyright infringements from black hats.
But I had no way to know Google was hating on them (and another hugely infringed paged that had been picked apart and blogged paragraph by paragraph in some cases) until I moved them to the Panda beloved site, where they didn't recover.
The way I see it, pre-Panda, Google saw those tens of thousands of infringements, made a notation that the content of these pages may not be original, but the overall status of those pages (one was PR=6, the others PR=5) and the site told Google that it must be the original.
Panda came along, looked at the same information, and decided that the site was featuring suspicious content and demoted the entire site. So the traffic to all of the pages fell by roughly equivalent amounts, and it was undetectable why.
Finally, when I 301'd the pages to a site Panda loves last month, Google still saw those "unoriginal" pages as an issue and in a ranking change that's happened at some point in the last 10 months, decides that unoriginal pages don't deserve much traffic despite their authority. So even with all the organic linking, they don't recover like the other pages.
I then reword them, and I mean I rewrote every sentence so that they say the same thing with different words and different expressions, and "poof", the traffic doubles the moment Google respiders them.
So I did something I swore I'd never do and started a serious rewrite effort on my lesser Pandalized site because at this point, I was just curious to see what would happen. Rewriting heavily infringed pages with similar pre-Panda traffic to the ones I talked about above, in a related subject area, had no noticeable effect.
The way I see it, the Panda penalty trumps everything else that goes on, and until/unless Panda reevaluates those sites, replacing the duplicate content has no effect. But when moving pages from a Pandalized site to a non-Pandalized site, the pages that Panda hated will stand out like sore thumbs.