If you run Numbers and Pages at the same time, separate instances of com.apple.MediaLibraryService are generated for each process, and each file grows to consume an enormous amount of memory. Notice also that the Numbers and Pages apps themselves consume an inordinate amount of RAM, far more than the '09 versions or even MS Excel and Word.
After a reboot and launch of Numbers and Pages, with the apps sitting idle, the following files climb over 20 seconds or so to the following:
com.apple.MediaLibraryService, 1.35 GB (first instance)
com.apple.MediaLibraryService, 1.35 GB (second instance)
Numbers, 568.8 MB with 3 small spreadsheets
Pages, 507.7 MB with a single blank document