From an engineering point of view:
By increasing the diameter of a pipe (e.g. conduit) by 50% the area increase 125%. However, the material used increase by only 50%, assuming the same wall thickness. If you were to put two of the orginal pipes side by side, the increase in both area and material would be 100%.
I doubt oversize conduit is a big environmental load. Oversizing cables is a bigger issue I think, as copper is not very healty. Nor is PVC.
Peter,
I think tree huggers are good for the electrical business: Electricity is (or at least looks) clean and its share of the total energy usage increase every year. If this development continues, everything will soon run by electricity.
The Arabs have realised this and are investing in solar power and power lines to export electric power.