The meth/water injection kits were designed to AID an intercooled setup to wring just a few more ponies out of a strip car. Not to be the sole means of charge cooling. That's all it is, nothing more, nothing less. If you want a little bit of insurance against detonation on a non cooled, mildly boosted, safely tuned car then I would say go for it. But trying to nail 470RWHP from an uncooled setup just does not sound like a good idea to me for a street car.
"Posterity! You will never know how much it cost the present Generation to preserve your Freedom! I hope you will make good use of it. If you do not, I shall repent in Heaven, that I ever took half the Pains to preserve it."