The point of higher octane fuel is to avoid Knock/detonation.
It really is up to what people do with their cars. The way you drive it really makes a huge difference in what fuel you should use. EVEN on a stock 4G64. I drive my car HARD. I revmatch a lot and I heel-toe alot when I am going on spirited drives. Not to mention my car sits at 3000 RPM's @ 75 when I am on the highway. The car is driven the way it wants to be driven.
I agree with Adrian that the engineers design the engines to run on a certain fuel for a certain application, but the manufacturer recommendation is the BARE MINIMUM.
87 is good with bone stock 4G64's that are daily driven under normal conditions. i.e. driving like how a regular owner (non-TGC people) drive a Galant. Not everyone will modify or even drive their Galant past 3000 RPM.
In my case, I run 93. And save the "wasting your money" argument because I am not buying it.
When it was auto, my dad ran 89 in it. and when I started driving it some more I used 89/93 sometimes even 87 and I didn't feel a difference.
Now that it is manual I run STRICTLY 93 in it. The only thing I have done to the motor is an axle-back exhaust, intake and a V6 TB. I run 93 in it because it has a SIGNIFICANT difference between 87 and 93.
On 87, you can feel the engine work harder and detonate through the dash. If you watch it idle, the engine vibrates A TON more on 87 than 93. Going through the powerband in 2nd and 3rd (not much in 1st, it goes by too fast) the car is significantly more sluggish and the drop of peak power is felt earlier than when running on 93. It hit peak power at about 5800 RPM on 93 and you can feel power drop at around 5500 on 87. The car is also stronger and has more pick up from a 60+ mph acceleration on 93 in fifth than it does on 87.
I run 93, to me I've proved its worth just by how the car reacts to my driving.
It could also be due to my adaptive strategies that the car runs better on 93 due to the fact that I STRICTLY use 93 and nothing else but thats besides the case.
I feel a SIGNIFICANT difference. So I stick with what feels better. I wish I had a dyno or a datalogger to see the numbers to prove my point.
"Fuel is all the same 'til they get to the pumps" is a fact but not EVERY car is the same.
The engineers design these motors to run "properly" on a minimum fuel grade, it doesn't mean the engine will not run better on higher octane. EVERY engine knocks, I dont care if it's a 1.3L from a Honda Fit to a 6.0L V8 from a GTO. If I can prevent my motor from detonating that much more I am going to spend the money on doing it.
It amazes me how some people can spend money on wheels, JDM parts, all these expensive mods on their cars but they are content with running the BARE minimum in their fuel systems, coolant, trans fluid, oil, etc. Just because they think running anything above the minimum is a waste of money.