The octane rating will have nothing to do with dirty fuel, gunky injectors, clogged fuel lines or polluted gas tanks. Very simply: It relates to the ignition temperature (Heptane, iso-octane, blah, blah, blah). The higher the octane rating the higher the ignition temp (i.e. 87 burns at a lower temp than 93). High compression ratio engines typically have a higher head temp, therefore the gas ignites before the chamber is sealed, blasting the valve train, causing pinging (valves being forced shut). It is also not an energy measurement, so you won't get better MPG with higher octane.
If you drive hard or with the car under load you may notice pinging, or "pre-detonation" with low octane fuel. The SC400 1UZ-FE engine is 10:1 compression ratio, which is pretty high. Your pedestrian sedans run typically around 8:1. If you are a leadfoot speedracer, you'll probably benefit from a higher octane rating in the SC400. I'm a very reasonable daily driver type, so 87octane does me just fine.
I do recommend buying brand name gas to avoid polluting the system. I have no favorite, but feel comfortable with Shell, Texaco, Chevron, BP, etc, but am uncomfortable buying from no-branded convenience stores and Bob and Malinda's shop and go...