Well for instance, the sprint pipe would benefit from normal mapping, but if weren’t vertex-lit then it would look absolutely terrible.
Even so, I reverted the pipes to being brush-based, since I felt that making them out of brushes brings the best balance of detail and lighting control. Brush lightmapping is far easier to handle than model lighting. I kept the pipe frame as a model though, since it doesn’t really need overly detailed lighting.
EDIT:
As an afterthought, it kind of makes sense that vertex-lighting is fundamentally incompatible with normal mapping. Normal mapping requires a light vector to function, which you can’t get from vertex-lighting because light is calculated as a scalar quantity for each vertex on the model.