Trimming the thin pages, with or without the Farmer algo, is a good idea. Imagine writing a technical paper, perhaps a thesis, with one word in 50 mis-spelled. That's the effect, for me, of running into a 'thin' 400 word post / page at intervals as I am reading online. Yank 'em and be thankful that Google caused you to review your site. Once they are gone, if the site doesn't begin to percolate upwards, you will at least know that all the remaining pages are strong, so some other factor must need attention.
My traffic hasn't been affected at all. It was, and remains, dismal. :-)