IMO the biggest benefit in a turbo application is the ability to run a much more numerically lower gear than a N/A motor.
Also, I don't think an N/A motor with a fairly healthy cam is going to be as efficient at lower speeds than a relatively "stock" cam that a turbo uses.
Finally, a stock type converter can be used vs a higher stall of an NA application.
This is the best argument for the turbo engine. My understanding is(and I could be wrong here) that the OP was thinking of adding a turbo to an existing engine to gain fuel economy not to add power. My stance is adding a turbo to an engine wont make the engine more fuel efficient. But as you say here the car can now be changed to take advantage of the turbo engine characteristics. I agree, if you want a 600hp car this is the way to go. If you want a 400hp car,not so much.
