Multiple angles to look at this.
1) MPG
I get that most of you want to look at it from this angle. Fueling costs are one of the most significant lifecycle costs to car ownership. Yes, there's some efficiency advantage to higher octane fuel, but the reality is that one will never see the added "value" from premium fuel in terms of mpg.
As noted above, non-corn fuel is a bigger differentiator here. Funny thing is that ethanol itself is higher octane (>110) than typical petroleum fuel. But less energy content. So the fuel industry is happy to use it to get the right higher blended octane. Essentially using cheaper filler, that makes higher octane gas, that they can sell you at a premium, yet results in lower mpg. Raw deal for us consumers!
2) Engine wear
This is specific to the LX570 that "requires premium". It's all about engine software calibration, specifically timing. This is not about turbo, or not. NA engines are calibrated to run right at the knock threshold also, as that's where the greatest power, efficiency, and emissions lie. An engine calibrated to run on high test fuel, will run a timing map, that when run on low octane, WILL knock. The only way the ECU knows that low grade gas is being used, is by experiencing knock. Only then, will the ECU back off timing. Only to ramp timing again, and hit knock. Rinse and repeat. Every knock event is added wear and tear. It may not be significant knock to where the user will hear or feel it. But it will be there. Just like the human body will run on junk and fast food. Overtime, it catches up to you. I've tuned NA, turbo, and supercharged engines and they all follow the principle of timing advance, load, and knock. If you'd have seen the readings and logs firsthand, you'd feel differently. Again this is specific to vehicles that "require premium". "Recommend premium" or "87 octane" owners can happily run "junk food" grade gas without consequence.
