Adwords data is best handled by a database. Spreadsheets like Excel just don't cut it. They are not meant to do the sort of thing you really need to do. You got to use the right tool for the right job: don't use a hammer to saw wood.
I download the daily stats into my database (I use Foxpro since that is my specialty). I therefore have the highest data resolution possible, at least what Google provides: each day's data for each keyword and each ad. It's then a relatively simple matter to run queries (reports) based on all sorts of things to help me optimize a campaign on many levels.