Photos, music, iMovie/iDVD/Garageband projects are stored separately from the application precisely to avoid any hassle that would arise from having to uninstall/reinstall. What I would recommend doing for a clean install of iLife is removing the applications from the /Applications folder, as well as their associated files in /Library/Application Support, and also the receipts packages from /Library/Receipts. This will ensure that there isn't anything lingering on the drive to come back and bite you just when you think you've reinstalled correctly. Also remember to run updates before trying to launch the reinstalled apps. The whole process shouldn't take more than 15-20 minutes including time for updates.