Ok, I'll try to explain Meth injection systems as best as I can.
In the older days of turbos people would use C02 to rapidly cool the intercooler so that it would cause a "freezing" effect on the air that goes through the intercooler to help lower the IAT's (Intake Air Temperatures). Lower IAT's will cause a more dense fuel/air mixture and give more power. This is why all cars feel like they have more power in the morning when it's colder than in the middle of the day or evening, because in all actuality they are more powerful. It's more noticeable for FI cars than NA.
Now in more recent years, Methanol/Water Injection systems have actually come into play. Yes they can make you lose power if you are using too much as it actually floods out the system. However, when spraying the optimal amount of Meth/water mixture (80:20 is a good mixture and lph depends on the boost levels), you will gain much more power than imagined. Meth/water injection systems have been proven to drop IAT's by about 40-60 degrees normally. This usually equates to roughly 40ish whp. HOWEVER, with it dropping the temperatures that much, it allows for a more aggressive tune to push more power out of the car. In a nutshell, Meth/water systems are just about as good at e85 when tuned properly. Most people have seen on average of about 50-60whp gains using methanol. However, if not setup properly, especially safety wise, you can blow your motor VERY quickly by running the car all out and not have any methanol in the system causing you to way over strain your motor and getting all kinds of knock or detonation which will cause very bad things to happen in your engine.
If I were you, I'd be contacting a tuner in your area to help you go over your Meth injection setup to make sure it is properly tuned and installed correctly for your car. If not, you will be replacing a motor very soon.
Also, 70:30 mixture of Methanol is actually Windshield washer fluid.
Most people don't know that.