To respond to this whole thread of discussion, what it seems to me is that NVC is a quite useful tool, and negotiation theory is the toolbox and instruction manuals.

It also seems that NVC could be a better designed tool (that's not to say that it won't do it's job!), and that negotiation theory could be a better formulated heuristic of when to use the NVC-tool, and when to use the other tools...

My concern is now cutting the cruft from both and adding the useful bits into the repertoire of my own rationality.

I'll have to look into them both further before I make any more in-depth of a comment than that, though.

ETA: Any recommendations on where to start reading up? (Free/online preferrable.)