Planet13 - 2:27 pm on May 28, 2011 (gmt 0)
...many detailed top-ranking pages with unique content are suffering alongside everything else...
Are those pages that are unique and were previously ranking high linking out TO the lower quality / duplicate content? If so, I would seriously consider removing links to your shallow content until you are able to improve the content of those shallow pages.
However, this is just pure speculation on my part, and I have no proof that it actually makes a difference.
We do know that if you have a good page that links to bad pages on OTHER websites, the good page on your site has an increased chance of suffering in rankings (hence, the development of the nofollow tag).
So by extrapolation (I think that is the right word), then maybe linking to shallow content on your OWN site from good content can hurt the rankings of your high quality content pages.