Do you also run a bottle of injector cleaner, or 10K Boost, or EGR cleaner, or any one of other much more potent cleaners through the car system as well? They will make a billion times more difference than switching from supermarket to premium fuel will.
Not saying I completely disagree with your logic: Indeed, I sometimes run a tank of 97 in the MR2 instead of the usual supermarket 95 for a similar reason, but then I also back that up with a good dose of the hard stuff once in a while.