Disclaimer: I am not a chemist, and I have little scientific knowledge of this subject.
My understanding is that methanol is used largely because is it combustible (whereas water is not) and that it has a very high octane rating (114).
The specific heat capacity of water (it's ability to absorb heat from its surroundings) is much higher than methanol; 4.18 KiloJoules/KiloGram/°C at 25°C as compared to 1.45 KJ/KG/°C. What this means is that a given mass of water can absorb roughly three times as much heat energy from its surroundings than methanol, regardless of where this absorption takes place (in the intake tract vs. in the cylinder).
The enthalpy of vaporization of methanol is about half that of water, meaning it's more likely to transform from a liquid to a gas inside the intake pipes, so perhaps that's where the assumption you posit comes from.
Of course, this is all a lot of theory with no application.
From a practical standpoint, I run a mixture of roughly 50% water and 50% methanol. I purchase my methanol from a supplier of racing fuel in 5 gallon quantities, and each five gallon bottle lasts quite a while.
Why do I run 50/50? Probably because I read that a bunch of other people do also.
With regard to nozzle placement- if you are running an intercooler, the nozzle should be placed after the intercooler. Injecting water prior to an intercooler will pre-cool the air and prevent the intercooler from doing its job.