Vectorworks' Renderworks module is powered by the CineRender engine from Maxon. As such, it is completely 64bit and can take advantage of over 128GB of RAM and multiple processor (CPU) cores.
However, this only affects the Renderworks-based modes specifically. OpenGL, Wireframe and Hidden Line do not utilize the CineRender engine, and thus not capable of using as much memory as their Renderworks counterparts on a powerful 64bit machine with plenty of RAM and multiple CPU cores.
The chart below lists each of the types of rendering mode, as well as if it uses your Graphics card (GPU) or if it depends on your processor (CPU) to perform rendering operations:
Rendering Mode Uses Graphics Card (GPU) Uses Processor (CPU)
Wireframe Yes Yes - Single Core
OpenGL Yes No
Hidden Line No Yes - Multi Core
Final Quality Renderworks No Yes - Multi Core
Fast Renderworks No Yes - Multi Core
Custom Renderworks No Yes - Multi Core
Final / Shaded Polygon No Yes - Single Core
As you can see from the above chart, the only rendering modes that will access your video cards resources is OpenGL and the basic Wireframe mode. None of the other rendering modes are dependent on it at all, so upgrading your video card will not improve any rendering speed or quality with any rendering mode other than OpenGL and Wireframe. (Note: your video card is directly relied upon for Top/Plan view and general navigation graphics in 2D, even though that is not a rendering mode.)
Conversely, the Renderworks-based modes primarily use your CPU and are capable of utilizing multiple cores. So to increase rendering speed in those modes, a superior processor (CPU) would be beneficial.
Wireframe mode tends to benefit from both upgraded video cards as well as a more powerful CPU, however it is more heavily dependent on the graphics card.