The belief that a 3D workspace is superior to the reigning 2D-desktop is an interesting one. Regarding visualization problems, I don't think that a 3D interface is drastically better than a 2d interface. Remember also that the data that we want to visualize may have any number of dimensions. Here's a half baked hypothesis, for instance.
Data presentation becomes an increasingly difficult problem as the dimension of the data increases.
So yes, a 3D workspace provides a little more power - if your visualization domain is limited to the surfaces of 3D volumes or is sufficiently scattered 3D points then it would great. Of course there are many such domains and many will benefit from interfaces that provide immersive 3D workspaces. However, thats just the tip of my iceberg of data.