Str82u - 3:00 pm on Jan 11, 2013 (gmt 0)

Why not update it moving forward? So, rather than changing the old threads that are historically 10 posts per page, just switch to 20 for new threads and leave the current ones 'stable' as they are...

That's more like I was thinking if it's possible for you to do with your current set up. More text and better content per page might raise the value of the current "page 1" pages but if you saw a drop in ranking due to 404s then you know what to expect as far as damage AND damage recovery.

As @Sgt_Kickaxe mentions, the paginated pages will have some duplicated tags and possibly lower search engine value but they could be worse as a collection of 404 errors. You would be the best judge of that since you know how you cleared up the Discus caused errors - would it be that easy?

one thing though - using your tracking - how much traffic are you getting past the first pages of each thread/discussion?