The higher the octane number, the higher the cylinder pressurre and temperture can be with out exploding prematurely, pinging. Buying more octane than you need will only cost more money per mile unles:
If the octane booster is methanol or ethanol, those boosters remove water from the air and disolve it in the fuel system which will corrode it quickly. Pure methanol cars have stainless steel fuel systems.
If the Octane boost comes from ethyllead, that chemical will poison the catalsyt in in the exhaust system and the EPA can fine people $25,000 for puposely ruining the catalyst. Also, the catalyst will breakdown and eventuually cause bakepressure and loss of power.
The main reason you can't use aviation gas or other non-pumped fuels is.. The goverment hasn't collected taxes on it . A long time ago, the oil companies were required to color the gas once it was metered and the taxes were paid on it. Many of people ran free gasoline in the oil production areas of the US and the police could stop the car and check for the colorization to see it the state had collected it taxes.
The octane in gasoline used to been increased by addition of cyclohexanes, notabily benzene (104 Octane), but benezene is being reduced because of suspected links to cancer so the search goes on for the best fuels......