Personally, I would copy everything under the /garmin folder just in case.
I have done that for all my GPSes including handhelds. It saves me having to re-install all my maps as well. However, if Garmin gives you a new GPS, you will still need to reinstall the maps with new unlock codes.
I had a problem with my maps (the latest voices were very strange and no-one at Garmin was available to help at the time - and I thought it could have been the voices I installed from the Garmin site) so after I retrieved all my tracks and such with MapSource and then saved them I used Windows Explorer to copy all my Zumo folders to my portable (I always have 'view hidden' enabled in Explorer) and then deleted the Garmin directory.
Then I recreated the Garmin directory and copied GarminDevice.xml back into the directory and ran WebUpdater.
This put everything I wanted back on the Zumo except the maps but I had the download file for the latest maps on my machine (remember they are unavailable from 'My Maps' on the Garmin site shortly after you buy them so make sure you have a copy before you delete anything) and then after I ran this I them had a functioning Zumo with the right maps but the voices were still wrong - but a web update a few weeks later fixed 99% of that.
So you can completely clean up a Zumo as long as you save the GarminDevice.xml file as it has everything you need to identify your Zumo.
Of course YMMV but this worked 100% for me and when I spoke to Garmin they were going to suggest this process.