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. [Linked Image]

The Arabs have realised this and are investing in solar power and power lines to export electric power.