The simple reason why the X-37B draws so much attention is that it has a classified mission.
NRO on-orbit ops are classified as well but people have become fairly comfortable in speculating what the mission is based on history, launch site, launch vehicle, orbital parameters, etc..
The X-37B does not have that history. OK, it launches from the Cape and flies on an Atlas V. And the X-37 started out as a NASA program, but that sample size and background are pretty modest.
So the real reason the X-37B is classified is driven by one thing: its modest capabilities and mission set are classified due for political reasons and not for technical reasons.
You just don’t have technical/capability breakouts that are delivered by what’s basically a sub-scale and unmanned space shuttle with a payload bay the size of a pickup truck bed.
What you might have are procedural breakouts; changed ways of doing business (or doing things) in space that might make some of the world uncomfortable.
(screen shot from Space.com, http://www.space.com/11006-air-force-x37b-space-plane-secret-launch.html)