To give you a 100% honest feedback, i had methanol injection in another car of mine in the past.
I call methanol injection "mini Nitrous" cos when you have it activated, you notice a noticable pull, its highly noticable.
On the car i used, non intercooled, i could boost safely/efficiently to 14psi, anything above that, it would be a wsste of time. it would ping at approx 17psi. When i installed the methanol injection system, i boosted to 20psi, with no problems at all. So you see, you can add plenty of boost in conditions that you would require a intercooler.
I have considered installing a kit to my starlet to make it even faster, but maybe later.