Been trying to pull together a taxonomy of 3D data viz. Biggest difference is I think between allocentric (data moves) and egocentric (you move) viewpoints. The difference between whether you then view/explore the egocentric 3D visualisation on a 2D screen or in a 3D headset is I think a lesser distinction (and actually an HMD is possible less practical in most cases).
We have a related benefits escalator for 2D->3D Dataviz, but again I'm not convinced that "VR" should represent another level on this - its more of an orthogonal element - another way to view the upper tiers.
Care to discuss or extend/expand/improve?