Sgt_Kickaxe - 6:23 pm on Jul 15, 2011 (gmt 0)
It may be tempting to make an odd change or two to older pages but it's just not worth the risk if that page is getting ANY traffic from search. Unless there is a glaring reason a page may be losing rank it's best to leave them alone.
This, unfortunately, applies to the index page and all category pages too. Simply adding new content to a site that hasn't changed in a year can be enough to send your traffic plummeting.
It's apparent that the perceived value of a page increases over time if it remains unchanged, and if the link structure proping it up also remains unchanged. I've seen FAR TOO MANY sites take a beating after having done well untouched for the longest time. Even minor improvements may have the exact opposite effect.
I figured I'd better put this warning here since it doesn't exist in Google's documentation.