The successful approaches I know about always seem to include a focus on conversion optimization rather than traditional SEO methods. Focusing on the user experience with a strong value-add for the visitor seems to make a big difference.
That's what I was doing on all my sites when one - just one of them - got Penguinized. Of course, most people here dismissed me as a lying spammer when I first said this, but I'm hoping the past year has convinced some that it IS possible to offend the algorithm without knowing precisely why.
That said, Tedster, assuming you believe me, what would you advise? Maybe exploring different conversion optimization tactics than I was using before? (And that has happened naturally in the past year, as I'm always trying new methods.)