tedster - 3:01 am on Oct 16, 2012 (gmt 0)
In a related observation, other pages on our site DO rank for the same phrases our older content does NOT rank for any longer. Different pages can be found in the top 30.
Thanks for that observation, @mhansen. So at least in your case, the problem is page-specific and not keyword-specific.
Do you think the demoted URLs being a "main menu" page is part of the issue? If so, does your main menu use text links that are loaded with strong keywords? Also, how many links are part of the menu?