Looking directly at that page I think that your reasoning is sound about adding an 'about', 'testimonials' and a 'review' section on each page. Strengthening those specific pages would do wonders in terms of the 'Participating in affiliate programs without adding sufficient value' bullet in the quality guidelines. In addition - adding more value and text to the page would improve the pages landing potential and fill in a SEO oppertunity that is often overlooked in this kind of funnel page.
Another possible issue of note is - seen upon a simple 'site:domain.tld' search (and there are a lot of pages indexed from the site already so what effect are you noticing from the Google penalty?) - your title tags, again mentioned in the quality guidelines. Most include site title at the front and not much else after. Optimizing those tags is something else I would do and above all else the page title text is a valuable SEO commodity not to be missed out on. Make better use of those titles would actually be my first move now I think of it.
There are probably a few more things about the site that could be addressed but at the moment I shall need to leave a more thorough dig till tomorrow as I'm a little pushed for time and, I've just come to the realization that, the capabilities on an Android tablet for testing are seriously lacking.
Sorry we've not, as of yet, manage to narrow the problem down to a specific reason. Have you created a campaign for the site yet? A crawl might give some insights into other possible causes.