whatson - 2:16 am on Jul 18, 2011 (gmt 0)
Google doesnt want to give away any details on how they rank our sites and pages. Therefore perhaps making changes will not improve your rankings on its next cache, otherwise you would have webmasters tweaking every single combination and permutation there is to improve their rankings.
I have changed pages with negative effects, and I have changed pages with positive effects, new and old. So as usual, you can only go on speculation and opinions.