The user rights log is nearly illegible when a user has multiple rights. Instead of listing each entry with the wording "...changed rights from A, B, C to A, B" we could offer a diff format.
The diff format offered by XTools:
Viewing the full log for a user suggests we would need a fundamental UI change with how logs are shown. Perhaps instead it'd make sense to duplicate the rights changes log on a dedicated special page (e.g. Special:AbuseFilterLog), called say, Special:UserRightsLog? Then we'd have the freedom to format it as we wish. This would be log shown at Special:RightsChanges. Some other core MediaWiki logs that change existing values may benefit from the +/- design, such as the protection log, with messages like "So-and-so changed protection level for ..." where it doesn't state what the previous protection level was.