There is a lot more to 3D than just perspective drawing. Illumination, shadows, etc mean that components of a picture interact with each other in a way that requires much more intensive processing than 2D. This means that it is a question of balancing the effects you would like to have against the limitations of the equipment, and making compromises. Personally, I see the future of GUIs not in 3D realism but in the accumulated ideas of art history. I include cartoons, morphing, pointillism, abstract art etc. That certainly seems to be the way that games are going.