I use Xara to draw all the profiles I need to use within the 3D application. Even in NURBS applications that are very good in 2D drawing I also use Xara.
Than I export this splines, profiles, whatever you want to call it, in *.ai, so the 3D can read and import the file. This splines become actual geometry used in the 3D.
Trough extrusion, lathe, and other spline rotines and with the further possibility to transform
the shapes to polygonal shapes you go deep in shaping the forms.
Everybody knows blue prints. So if you draw in Xara the blueprint of an object to represent a side view, a top view and a front view of the object and you take it to the 3D app, you have established the boundaries in space to draw that object.
Basically is what you do with Xara3D at a very limited level. Or with the new 3D tool in Xara Extreme.
This kind of workflow is very common among illustrators and is no secret our outstanding technique. I also use Xara to generate all my textures to map the tridimensional objects and the alpha channel trough *.png format is very usefull to "cut" the graphics.
The screenshot of C4D is to show how the splines become geometry after the proper manipulation.
I hope to have been explicit.

Emanuel