I've dealt with methanol injection on turboed cars, more specifically on a 2.5L EJ257 STi where compressed air heats rapidly due to nature of turbos and heat soak. However I do not foresee any naturally aspirated application worth the risk of hydro locking motors with failed valve stuck open, or motor going way lean when the valve stuck close. There are plenty of check valves and safety measures but in case something goes wrong, the gains are too minimal compared to the risk that is undertaken. Personally would keep it purely on forced induction applications.
The benefits are actually very major, especially with additional cooling capabilities, of atomized methanol drops turning instantly into vapor before actually entering the combustion chambers cools the intake charge quite a bit, so think of it as an additional intercooler in chemical form. And the higher octane of the methanol fuel itself allows boosted application to run quite more pressure on pump gas, that is where the power is gained, the abilities to run say 3-4psi means 30-40whp on my application. Power gained are much higher on other applications where boost can be cranked even higher, say an EVO 8/9 with cams, power gains are signifcant enough to justify the risk of methanol failure. It is essentially playing with fire because mostly cylinder heads are alumium, or worse yet the entire block is composed of aluminum and methaol is corssive to alinium. Another problem is the lower boiling point of methonl, and its natural tendency to absorb moisture out of air, so keeping a dead on air-fuel ratio is hard if the fuel itself is changing properties. Lastly methanol also dilutes oil, so in case it is not 100% burned off, it will raise havoc on oil and recommend much lower oil change intervals.
Those are my findings.