This is what I was told regarding octane and the AA tune from the authorized shop that did my install:
The stock motor has the ability to run low octane fuel (91 or lower) and still get around. The engine software could adjust the ignition parameters to make it "work" and not leave you stranded on the side of the road. Ultimately you would get the best performance with 91 but you still had the peace of mind knowing that 87 would get you around if you couldn't find 91. The AA tune now requires the 91 octane as a minimum with a slight benefit with 94 octane (1/2 hp at most!). It optimizes the ignition parameters to maximize power with the better fuel. You lose the ability to run crap fuel in your car but gain a bit of power. Just my 2 cents.
Aside: What are you doing cheaping out putting 87 in your car!?!?! The owners manual clearly states 91 octane. And you shouldn't be complaining about fuel prices! Canadians pay $5.30 /gal for premium! I bet the shiet fuel has to do with your poor fuel economy. I get a solid 25 mpg (calculated, not assuming the computer is correct!) with a mix of 50/50 hwy and city driving and that's not exactly granny driving.