Hi Chris,
"""""""""""" I fail to see in many situations where the nurbs is actually going to better to machine from where there is a lot of surface variation.""""""""""""

The NURBS will be preferred by your CAM system. With a NURBS model, you are allowing your toolpath generator to perform the path calcs and decisions with regard to the settings within the CAM system.

With a poly model, you will be forcing the toolpath calcs, tolerances, moves etc, in conjunction with the CAM settings, which is less desirable and can be problematic when you are doing precision work (especially molds)

Frenchy mentioned reducing the poly count, which I do a lot. The programs today are getting really good at this, but there are some considerations (mostly with molds)

Is DOES morph the intent (but so does the NURBS conversion), so if you are doing 2 part work, you will want to re-create the second/split half from the morphed result. The "decimation" can be done to allow for tolerances specked on the part.

I use 3dcoat for poly retopo's or "decimation".....