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.
If you switch on the Ambient occlusion and use the default settings, you will notice the defined corners, but it also made the scene darker and noisier.
To restore the brightness of the scene, you need to reduce the radius of the ambient occlusion. The walls and ceiling have brightened up by reducing the radius to 3 meters, but the scene's noise is still distracting.
There are various ways to reduce the noise in this scene. The most direct way to reduce the noise is to adjust the Subdivs in Ambient Occlusion. Increasing the Subdivs to 16 improves the scene's noise and enhances the corners and joints details.
Turning Vray Ambient Occlusion enhances the details in the corner and joints. Depending on the complexity of your scene, render time may increase a bit. Since this scene has only a few objects, activating Vray Ambient Occlusion has not dramatically increased the rendering time. Although there might be a slight increase in rendering time in scenes with many items, the results on the final render using ambient occlusion is worth it.