I've read a lot of reasons why this tactic might fail ranging from being deemed spammy to being duplicate but I think there is a more simple answer, post Panda.
If/when you add thousands and thousands of pages those pages will become instant competition for your own keywords. If you had one amazing page for any given keyword before the new content there is a good chance a page of the new content is deemed "the best" by a bot.
If one of the new pages replaces your old proven article for any given keyword it will rank according to its own merits which might actually result in a LOWER position for your site on that keyword.
When adding pages in bulk its extremely important to have any page which might be a competitor for a keyword you already have to point to that page with a link.
If you perform a search for a specific keyword you rank for and you are #1 try another search with the site parameter and that keyword and see how many pages return, less is more sometimes. You can take the search further and exclude your known #1 page to find out what your #2 page would be, and where it would rank, by using negative operators. Linking the #2, #3, #4 etc to the current #1 seems to provide results. They are related in the eyes of google so the links make sense on all fronts.
