D7000 - Dark Viewfinder?

Yes, but the overlay does not in any way "amplify" the photons coming through the lens-> mirror-> vf path.

It's only an illusion that the light from the overlay makes the scene more bright -which it does not. It's like putting a flashlight to point towards eye when you are looking at a dark scene. Your eye will receive more light, but the scene itself is as dark s before and you can't actually see more detail from that scene.