In this scene, the arches have UV image maps for color and bump maps, while the light colored curb directly behind them is flat color. The model was created in Blender and laundered through PoseRay. What am I doing wrong?
Difficult to say without seeing the actual object and file.
As a sanity check try re-UV-ing the object just to check it is in fact correctly working.
Also try using a simple chequerboard to preview the UV mapping.
I tried rendering a part of the model (literally, a chunk off of a copy) and it emerged free of artifacts. So now I am re-UVing the thing to see what happens.
Does it have any duplicate/overlapping faces?
I am finding several as I work along, yes. I created the structure (in Blender) on multiple layers, and assembled it for export with insufficient rigor, it seems. ::)