Virgin Atlantic is an exceptional case-study of how effective holistic branding can change passenger perspective in the Economy cabin, even when structural conditions are not significantly differentiated.

Exactly. They understood the human approach—the product wasn't that different but what surrounded it was. 

And coming up with Premium Economy was nothing short of brilliant. 

It must be affordable enough for Economy passengers with a little extra change in their wallets to spring for the upgrade, while not being so comfortable a product offering that it competes with the airline’s Business Class.