It's not the lighting that makes the image look dull. I'm not sure what "dull" stands for here, I think you mean sort of graininess in an image?
This is mainly caused by the simple fact that Vue can handle "only" 25 sub-rays. You can see it in extremely soft shadows and when using strong depth of field.
For comparison, Bryce 5 can smack images with 256 rays per pixel -meaning eternity-slow rendering but good quality of an image if other parts of Bryce-image are set OK.

I have no idea if Vue Pro handles more sub-rays -I was going to ask it when starting this post- so I can't tell whether images rendered with VuePro differ from Vue4-stills

I'm pretty new to Vueing around, but when I was asked to make an animation of tornado hitting a house, I had to choose between Lightwave and Vue. I chose making that 3second tv-spot with Vue because of the number of sub-rays -the grains gave the effect of dirt to be blown around. In action that meant lots of faster rendering with somewhat neat result.

Again, I'm new to Vueing and therefore don't know how "seniors" post-produce their still images with, but I've found that when making stills with strong DoF or soft lighting, programs like Neat Image Pro and Photoshop are my best friends: NIpro kicks grain out of the image and color correction and enhancement can be done in Photoshop.

Images in Renderosity's galleries, I think, are mostly made with only rendering image in Vue -if you post image through dozen different programs, the result is hardly an image only fitting to Vue d'Esprit gallery.

Hope this answered your question -even touched the topic:)

.mjt