I use diluted Optimum for wheels (light cleaning) and this diluted pro product (lye based) for heavy cleaning; I wouldn't use Optimum without rinsing.
I don't use steamer for interior, just a regular vacuum cleaner.
Power washer is half a hassle for me and I don't like the strong spray which may take off trim, paint, emblem, or any other piece; so undercarriage rinsing is done using a garden hose with a good nozzle. I do this several times a week between the truck and the Z in salty months keeping them cleaner, so a power washer is not required; they never got so dirty. Only once in a long while one of them would need a couple full washes to get rid of the heavier dirt.
I use a cheap 1.5-in wide paint brush (with a few layers of duct tape around the wide part next to the bristles to avoid marring and scratching) to clean between spokes and lug wells. A large soft nylon brush with split ends for larger areas like the lip and center section. To clean the barrel, I use a tire-bead-lube applicator which has loose cloth bristles and wire handle. The wire handle is covered by a few layers of duct tape to prevent marring and scratching. It's small enough to go between caliper and barrel for most wheel and brake conbinations; otherwise the car will need to roll a maximum of 270-deg wheel revolution (the case for CTS-V with 18" wheels, no need while having 19" or larger).
My interiors are usually vacuumed and lightly cleaned using this pro product containing mink oil. Once in a long while, cars with leather trim get Leatherique full treatment. So far, the Leatherique treatments never yielded anything to indicate heavy soiling.