Well it's mostly just a matter of bringing the mesh in and modeling the object as if you were building it from scratch. You can take sections through the mesh and draw on it, but then you have to clean those curves up.... To test your accuracy you use "PointDeviation."
I don't think a CMM's going to help much/any over a scan, it indeed won't be able to capture all the detail and will still give you a mesh...maybe if it's cheaper just to make a start.
Rhino Sales, Training, Consulting
www.hydraulicdesign.net