water injection is great.... for stupid powered cars. our street cars really don't need it.
the nx-cooler is a waste to me too. it works, yes, and makes 30-40hp on 500 hp cars... but so does 1 more psi of boost on a larger turbo.
filling the tank gets expensive and annoying.
my vote =- neither. if you built it right in the first place, and have a good intercooler that does its job, neither are required for a street car