A simple tip that can improve your renderings is to take advantage of Vray's ambient occlusion. Ambient occlusion wasn't available back when I started using Vray. Ambient occlusion is a simplified way of using Vray dirt in the scene.
The first scene did not use ambient occlusion. The walls are too bright, while the joints and the ceiling's corners aren't that well defined. There are also a lot of overblown highlights in the scene.
