(No pun intended regarding spotlights, lol)

I tend to answer questions based on my workflow, which is usually texture-based first, then I go to the lighting and start tweaking. But balancing ambient light and shadowing are indeed critical for the look of your render. This weekend I can post some examples in Vue of the differences lighting has.

Overall, it's been my experience in renders in both Bryce and Vue that ambient light, as left at default settings, tends to wash out the image, and flatten it quite a bit. So I tend to rely less on ambient lighting and more on direct sunlight, maybe augmented by some spot and point lights.