This really is a shame--it presumes one has a crystal ball to divine what, 20 years hence, may hold "historical significance."
Insofar as we are in the information age, why would we discount any information from an entity that deals with history in as significant a way as the FBI?
I am a retired FBI agent--to that end, I cop to filling my share of pro forma documents (the FBI is famous, or notorious, for having a form for EVERYTHING).
OTOH, as a current faculty member at a tier 1 research university, I recognize the necessity for information; and once something like this is gone, it's gone. Forever. And despite the good intentions of the folks who decide these matters, I'm not sure it's fair of us to place on them the weighty responsibility of deciding "historical significance."
Is there any reason we can't make an investment to digitize all this stuff? True, it's gonna be a big chunk of change upfront, but dang.