How much do intercoolers help???

Ok i am starting to save up for a power adder real soon prob in the next six months :banana: and the more i have looked into it i really like the idea of a vortech s-trim or a paxton novi 2000 :D . 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? :shrug: