I've seen this debate many times on the Prelude forums since the engines are mostly high compression engines 10:1 ratio's. Since the FRS/BRZ has a 12.5:1 ratio, which is very high, I wouldn't mess with the higher octane recommendation just to save a few bucks. Do you really want to rely on retarding the timings especially at high rpm's? Do you really want to wait until your engine knocks before switching to premium fuel? It may be called a knock but do you know what it's actually doing inside your engine? A knock is an early explosion inside your cylinders before the piston has reached it's peak (on it's way up on the compression cycle) because the fuel was ignited too early, either due to the lower octane fuel, higher temperatures, old engine, air fuel mixture, etc.. Just imagine your piston having to fight that explosion as it's trying to go back upstream like a spawning salmon. Maybe some people think a car is like a pet, it will get used to eating the cheaper food and some days they'll splurge, haha.
http://www.caranddriver.com/features/regular-or-premium