How much do intercoolers help???

Ok i am starting to save up for a power adder real soon prob in the next six months and the more i have looked into it i really like the idea of a vortech s-trim or a paxton novi 2000 . I like that they have a seperate drive belt and use a draw thru mass air meter. I was considering PTK or ATI but with the substational cost and wait (PTK) I think a paxton or vortech is a better overall choice, the only prob is you cant get a intercooler for our years with those blowers. How effective is water/methanol inj. and how exspensive does it get refilling? Also if you had water/methanol inj. set to come on at a certain boost level how could you tune the car to start leaning out and add more timing once it hit that certain boost level?

anyone? any advise or knowledge would be really appreciated