Linxv5 - Welcome back to WebmasterWorld. I'm sorry that your situation is still in the decline.
Worth noting that about three weeks before the article you cite where Matt Cutts' confirmed the penalty, there was a background explanation by Danny Sullivan, which looked at the many potential causes for a penalty. I'd suggest that it would be helpful for anybody following this discussion to read it, because it suggests how much everybody was surprised at the time, and the kinds of issues that Danny looked at on MetaFilter itself....
On MetaFilter Being Penalized By Google: An Explainer Danny Sullivan on May 22, 2014 [
searchengineland.com...]
A few thoughts, to get things started... In your post, you list what you've tried, and I'm realizing, at this stage in the game, that it's basically a list of surface mechanical details that might have helped with a certain level of thin-ness and some of the usual weaknesses of user-generated community sites.
Your list includes five items (I assume you've done more). It shows that you noindexed some of the types of pages that could be diluting your content (tag pages, member profiles) and that you've pruned some content, and cleaned up some pagination issues.
I've always regarded noindex as kind of a temporary band-aid for Panda, but not a long term fix. Too many nav links to pages that needed noindexing, even if that link juice is recirculated in the site, still result in an unsatisfactory user experience.
For that reason, I'm also not a big fan of tag pages as a substitute, say, for categorization and structure. I have seen tags used well when used sparingly on sites that are focused and very busy. But these are important mechanical issues, but I don't think they go far enough.
In your posts from the Nov 2012 WebmasterWorld thread you link to, you acknowledge that
"this is related to "low quality content" or not enough content, and maybe it has also some relation with duplicate content"... and that's what I think too... but you didn't mention what you've done to improve the content.
You also don't mention any larger changes in your site... enhancements to make your site stand out from the sites that are now attracting the kind of traffic that you once had. I would do a lot of test searching, and look at your competiton and compare yourselves with the best. I think I'd be comparing the site with platforms like Medium and Quora, which are actively encouraging the generation of quality content in areas that may overlap with you.
At this point, I think you need to be looking ahead... not dwelling on a 2012 penalty, which, rightly or wrongly, happened years ago. That's easy for me to say, not easy for you... I know... but I think it's necessary for it to be said. To be doing well, you really need an extraordinarily good site.
PS: One item your list...
nofollow for all external links
...jumps out at me because it may not have been a good idea. Can you clarify? I'm a firm believer in dofollow external links to good sites... and I've seen internal use of nofollow backfire badly.
You also don't say anything about inbound links. From what I've seen, gradual declines as you describe are a combination of weak content and bad linking, both inbound and outbound.
