footage never seen is always great to me.. I'll say what makes footage extra special is something different about it.
* set list different than usual
* dance moves he experimented with that day.. Often he has a sertain 'feel' that day.. more robotic, more fluid, etc. it changes up the feel per concert
* performances he doesn't usually perform in specific eras.. (Human Nature durring HIStory era / BAD durring Dangerous) that type of stuff
* rehearsal footage I always dig
* anything backstage, or 'not meant for public' stuff.. All day!
Pretty much anything that makes a concert or footage unique in some way.