I think it depends on how often the pages are promoted internally. If the "off the beaten path" thin pages are hard to navigate to, then it shouldn't be a problem. If you click around the site and get to both thin and fat pages regularly, then it could hurt.
I work with a site with about 30,000 pages. Of those, there are probably only about 1000 fat pages. They do a great job of promoting the fat pages to visitors, but allowing visitors to find the thin pages if they really want to.