Oh trust me, 89 octane does pay off... for me at least in my 05.
The cars in those years tend to run more timing than they can ever achieve, thus a quick fix outside of reflashing the ECU which 01s cannot is 89 octane. The increase in gas mileage overcomes the increase in price in most cases. I've been measuring for about a year now. On 89 octane, I can get around 30-32 mpg during long road trips. Quite nice. I measure for miles traveled on odo vs amount of gas filled to the top.