One of my large sites with more then 15k pages (not going to reveal my niche) has ranked well, its a shopping type kind of a site and google has ranked secondary pages for some of the long tail keywords. I haven't spammed it and only bought quality links, but with the penguin update and having to have only relevant links has caused my site to drop, so now its not ranking for the main keyword that I was targetting nor it ranks on the long tail keywords of the secondary pages. I've already invested alot in it and wondering if its still worth trying building and getting high pr links on relevant post to build an authority and get my ranking back? Or once its been flagged by google bothering with it ain't worth it? Please shine some light here, its very stressing. Thank you!