I have some scripts that can potentially help with saving any of your current artwork. The scripts have slightly different functions:
CreateFolderArt ensures that every album folder ends up with a Folder.jpg image which is the art that iTunes already knows about. Side effects are that if artwork has been updated in iTunes the folder art should be updated also, and if any track from the album doesn't have embedded artwork it gets embedded.
EmbedFolderArt was actually written for someone who already had various artwork images stored in the album folders and wanted them added to their tracks, but not if iTunes had already downloaded a better quality image. It creates new files of any store art with the name iTunesArt.jpg, then embeds the largest image by area in the album's folder, based on the premise that this is likely to be the best image.
EmbediTunesArt is an alternative for when your library might have tracks from different albums in the same folder. It creates a new folder called Artwork in the same location as the script and saves any images it finds in the form <Album Artist> - <Album>.<Ext>
And yes, you could simply rename existing Album Artwork folder to say Album Artwork (Old) and see if rebuilding the cache helps. If it doesn't delete the new folder and rename the old one to restore it.
tt2