Planet13 - 5:25 pm on Aug 4, 2013 (gmt 0)
When you say:
"I've tried for many, many months to recover a site slapped by Panda and penguin."
What EXACTLY have you tried?
If 70% of the traffic was direct BEFORE Panda and Penguin, I would seriously consider just keeping the old site. You said that you plan on building a new site from scratch, so why not just put the new content on the old site?
Is your home page the one that has the most bad links (that generated the Penguin penalty)? In theory, until you can remove enough links, if you get lots of direct traffic, you could have your home page serve a 404 response, but still keep the functionality of it for direct traffic landings.
Or you could make a new home page (/home.html) and again 404 your original home page.
aristotle had an interesting suggestion. As he proposes, I doubt that a penalty is passed along by a link from a penalized site to a different site.
On the other hand, I doubt much, if any, page rank is flowed TO another site FROM a penalized site (although I can't say that with any certainty.)