Hi Flamingo, & thanks! I hear good things about Rhino nurbs so you've got a good tool -- and that's half the battle right there
For Amapi, the only version that's really full-featured is the current release - Amapi Pro 7.52. And if you really want to get the most out of it, you'll need to lay out another $90 and get Marc Berry's training videos from VTC. There were large parts of the workflow that were a total mystery to me until I spent several hours watching Marc drive it. Now when I use it it's like putting on a glove -- I'm even starting to remap Carrara 6 keystroke commands to match Amapi because I keep hitting the dang things and nothing happens.
One drawback to Amapi is that you have to find another rendering environment and import to it -- Amapi is strictly a modeler, what rendering it does is only for test shots to see how the modeling's going. I'm using C6 because I've been using it ever since it was Ray Dream Designer 3.0, I'm used to it's quirks and it's actually pretty powerful and can produce a very photorealistic render.
Just last week I snagged a discount copy of the new ViaCAD Pro package, which also seems to be a very powerful nurb modeler. I'm thinking of tackling one of the Mercedes crankcases with it to get a feel for how it works.
More to come soon . . .