I used to be in the intelligence field, and I held a top secret SCI clearance for about five years.
What most people don't realize about classified information is that it's not the information itself that's so sensitive; it's the means via which such information is acquired that must be protected. If this were not so, targets could simply sidestep our intelligence collection vectors.
I rarely dealt with any classified information that was interesting or surprising. It's mostly stuff you would expect. The technologies and methods used to acquire a piece of intelligence were always more interesting than the intelligence itself.
It generalizes my original point better than I did: with classified material, the secrecy is always because of the how, not the what.