I suggest that SU materials also show reflections, similar to the way they can be transparent now. There could be an adjustment for different materials, so an approximate reflection is shown. This way water and metals could be realistically represented.
You want a renderer.
But a renderer will not help, I believe, because I do not want to produce jpg still images. I want all the 3Dness that is in my model, for animations.
You need a renderer, possibly one capable of outputting animations. What you want cannot be achieved in real time, it requires a raytracing algorithm.
catamountain and Anssi are right. SketchUp does shading and texturing, but to handle reflections the software has to trace rays to see what would reflect at each point on every surface (iteratively when the reflected object itself has a reflection of something else). That requires much different software and is not feasible in real time without really exotic hardware.
check out tutorials for the ‘LightUp’ plugin, it all works inside SU, but in a different [exportable] context…
www.brighter3d.com does this very fast worth a look. youtube tutorials