Wouldn't headers lower the threshold of boost pressure thus providing higher torque in the midrange? Thermal coating the headers would help keep underhood temps down.
Most quality headers aren't really cost effective but for those who are looking to extract more power on the big end end up getting headers. Boosted LSA motors ZL1 & CTS-V's pick up 17 to 20 hp and torque respectively with headers.
Whenever the aftermarket comes out with a HC pulley folks are going for maximum power.