Correct me if I'm wrong but there's nothing that can be done with polygon based graphics that can't be done with raytraced poly free graphics. Pixel shaders etc are simply attempting to emulate what raytracing has done for years.
Here's the main advantage polygon/shader rendering has over raytraced rendering: Speed.
For the same amount of perceived visual quality, polygons/shaders will always be faster than raytracing (unless some entirely revolutionary technology is created). This means that for the same frame rate, the visual quality of polygons/shaders will always be better than raytracing.
As technology gets faster and faster, this will still continue to be true - raytracing will lag behind polygons/shaders. For example, even though a raytraced version of "Crysis" might be possible at 50 FPS in several years from now, something 10x more realistic will be already out using traditional methods.
I'm not in the business but I'm pretty sure a lot of modelling is done using splines and nurbs already, it's just that it's rendered into polygons rather than kept as is. Mustang will know!
Just how do nurbs give you the extreme level of detail that polygons do? If you want super-realistic, teletubbies-like graphics, then raytraced nurbs and splines should work great. But for realism, smooth mathematical shapes just don't apply:
I'd like to see you render that with nurbs.