Hypothetically, assume for just a second that the opposite were true. You know from your LS430, another vehicle that uses the "required" verbiage, that there is an effect with using lower grade fuel. The concern isn't really about power. It's about knock events that the car's ECU is responding to. Less power is the secondary consequence to low grade knock, that over the long term can impact an engine. Or use it at the wrong time with heavy loads, hot weather, bad gas, and long term microscopic pitting and carbon build up due to uncontrolled flame fronts with low grade knock...is there margin left?
Is it wasting money? Is it marketing BS? Maybe
@Kilcarnup has a point?
The LC guys don't have a horse in this conversation. The LC is calibrated for 87. When I owned an '06 LX470, it was 91 "recommended" and I used that to my advantage. It tells you the ECU tune is setup safely for 87 and can take advantage of 91. I put 87 in it all day, with 91 for heavy towing work. Yet calibrations like this don't use timing tables that fully maximize higher octane because they have to walk a finer line against knock thresholds.