Heh, spray is $2-$4+ a pound, not gallon. And it would be much more beneficial IN the motor!! Small shot would get more gains and drop the intake temp. Say a 35 shot. Or can your motor not take the giggle gas!?!?!
If the nitrous is setup and tuned properly it won't wear on the engine. A small 35 wet shot would much more efficient cooling and much cheaper. Bottle would last a long time instead of pissing it into the air.
I understand he's at the limit of his injectors (not sure about Nissan but LS1 injectors will run 105% duty cycle all day long.) A wet shot jets fuel with nitrous through the nitrous nozzle, has nothing to do with injectors. My injectors run 80% duty cycle on motor and 75% on bottle (jetted a little safe on the fuel side.) Now the MAF concerns make sense since he's walkin the line of measurable flow. On the bottle it would be moving air a little faster and would likely push that limit.