I would also point out that U.S. law specifically criminalizes economic espionage on behalf of foreign governments, but economic espionage on behalf of the U.S. government is not illegal.
TL;DR: It's absurd to think that the NSA isn't spying for economic information. Tons of evidence has been presented.
There have been many, many stories published in the world's leading newspapers about NSA industrial espionage:
http://www.globalresearch.ca/nsa-busted-conducting-industria...
The NSA's own slides list "economic" as one of the main reasons for spying. And none of this is at all new:
https://www.fas.org/irp/program/process/991101-echelon-mj.ht...
http://www.motherjones.com/politics/1999/11/outfront-0
I would also point out that U.S. law specifically criminalizes economic espionage on behalf of foreign governments, but economic espionage on behalf of the U.S. government is not illegal.
TL;DR: It's absurd to think that the NSA isn't spying for economic information. Tons of evidence has been presented.