20 cents more a gallon for premium is hardly anything. Think about it; lets just say that you average 25 mpg in your FRS/BRZ. If you drive 25,000 miles a year (easy math) then thats 1,000 gallons of gas a year.
That means you are only spending $200 a year for the premium fuel when compared to if the car had run on regular. Thats hardly anything; its $3.84 a week.
I don't understand why people get so weird about money when it comes to gas. Paying 20 cents more per gallon to get more effeciency out of an engine seems unreasonable to people. People will drive out of their way to get to the cheapest gas station if it will save them 3 cents a gallon on gas. Its madness.