Benefits of alky are being able to run pump gas and 20-22 psi. More boost = more power, provided you have the fuel to support it.
If you didn't have alky you'd have to run lower boost (15 psi) on pump gas, or if you were to run 20-22 psi, you'd have to run race fuel, which gets expensive.
Alky is about the price of regular fuel, race fuel is usually at least twice that amount. Yes alky is safe on a street car, it actually burns slower than 93 pump gas.