Spraying Nitrous accross the intercooler cools the air charge more and that can equal power but I doubt it's very cost effective. When racing an intercooler can become heat soaked while sitting around waiting for the next run so I'd gather a nice cool down shot would help some. The Icy shock might not be so good for the intercooler itself tho but that's for someone else to ponder.
Spraying across the intercooler helps bring the air inlet temperature down, thus creating more horsepower because you can run a more aggressive tune. Most classes don't allow 2 power adders, so they spray the intercooler instead of the motor.
The NX kit actually added 27 RWHP when I had the stock motor with the P1. Sprayed in 4th gear only. Might have made more if I would have sprayed through 4 gears, but with a 5 lb bottle, it doesnt leave much to work with.