Fourth.

No more GI to reduce render time. Just the 2 lights and Mental Ray just to get the Blurred Reflection effect (quite render time consuming also)
I'm quite satisfied with look without GI.

Added:
Floor and wall Textures, Bump Maps
Grid Map to the Light Color to simulate shadows of a window
Warm (yellow) point Light at the center of the scene.
Teaks to the Blurred Reflections.

Problems:
Strange geometric spots appeared on both textures (wall and floor)
Overall lighting I think it's a little too dark (some friends said that the image was way too dark to see on their monitors).
I wanted to achieve some kind "if-batman-had-a-Harpsichord at-his-BatCave" Lighting mood, so I imagine it quite dark anyway.
Render time: Around 8 hours for frame. It's getting difficult to do the tests.