Too many new content -> lack of motivation to check all of them in one time.
Popular social networks have a functionality named as "Timer".
It is ability to make uploaded content visible only since some interval/exact time.
Maybe we could try to allow users/admins (selectable by access rights) to set an interval for all mass-uploaded files?
Works like this:
Mass-upload 20 images in one time.
Set interval - "2 hrs".
First uploaded image appears immediatly. Every other uploaded image from this upload would be published from time to time with configured interval.
For users: Ability to see something new every time visiting forums, because new content appear in gallery by portions.
For admins: Save the time by publishing all new content in one upload, but not overload users with it.