Wow, you're on a roll. That old chestnut has been incorrectly parroted on internet forums since the beginning of cyber time. A receiver pressurized to 200 psi contains twice as much air as one pressurized to 100 psi, so how again is that air "wasted?"
You are right that you can store more air in the same volume at higher PSI.
But we are talking about continuous output as needed for sand-blaster, not buffering for an intermittent tool.
At lower PSI single stage is more efficient. As I said earlier, don't take my word for it, compare compressors with same HP from same manufacturer that offer them in a 2 stage and a single stage configurations:
5hp Jenny Compressor with two stage pump:
15.5 CFM @ 100PSI
5hp Jenny Compressor with single stage pump:
18.3 CFM @ 100PSI
http://www.jennyproductsinc.com/portables/tswp.html
http://www.jennyproductsinc.com/portables/sswp.html
Single Stage and Two Stage Reciprocating Pumps
Reciprocating (Piston) Compressors can be widely found in two primary configurations; Single Stage and Two Stage.
Single stage air compressors work by drawing air in and subsequently compressing the air to its final pressure in single piston stroke. Single stage air compressors can attain pressures of up to 150 PSI.
Typically, a single stage pump will have a higher CFM(Cubic Feet per Minute) rating than a two stage pump because every cylinder is drawing in air and compressing it with air during every rotation.
Two stage air compressors work in a very similar manner with the primary difference being that they compress the air in 2 steps or stages. During the first step or stage, air is drawn in and compressed to an intermediate pressure. After being compressed in the first stage, the air is piped, usually through an intercooler where the air is allowed to cool, to be compressed in the final or second stage. Two stage compressors are normally good for pressures up to 200psi.
Two stage pumps are more efficient at higher pressures because the air is cooled between the stages.
http://www.jennyproductsinc.com/howtochoose.html
You misunderstand if you think more stages is always better. It depends on output PSI.