I keep such stuff *VERY* nice on all our vehicles. The approach varies a little depending on how pampered the vehicle is.
Painted surfaces are usually *not* be cleared and the paint is often thin, so go easy with the abrasives. For beaters I usually do one pass with 1Z Ultra/Extra (might oughta use a milder follow up on dark colors) then 476S. For good cars I use a milder polish then the regular (for that vehicle) LSP. I maintain with leaves-stuff-behind QDs or, on the good vehicles, UPP spray sealant.
Black painted areas seem to respond *very* well to BF polish and sealant, even if there's a bit of surface rust. Surprised me, but this is a near-miracle approach for those surfaces. I maintain with UPP spray and/or FK425. On some areas of beaters I use 1Z Ultra or AIO and 476S instead but you gotta watch that residual product doesn't leave white/etc. deposits that look crappy.
Rough textured body-color areas of the good cars get cleaned now and then with AIO (don't let it dry! buff off with a high-nap towel while still damp or you'll never get it all out of the convolutions!) and then sprayed with UPP spray. Ditto for large black plastic/fiberglass areas.
I clean the above areas with strong car shampoo at every wash, but on the beaters I'll usually end up using APC/wheel cleaner at some point in the late Winter as I'll be redoing them come Spring anyhow.
Painted calipers get sealed with BF and washed with strong car shampoo. Unpainted ones I just clean with the steamer once/twice a year and then wash with wheel cleaner/APC at every wash.
Plastic fender liners on the beaters I often do *not* treat, but rather just clean with APC/wheel cleaner at every wash. On the good vehicles I treat them with UPP and/or UPP spray (the S8) or tire dressings (less pampered vehicles). I clean the sealed/dressed ones with shampoo mix to avoid stripping it at every wash.
Rubber brake lines get ERV dressing or Autoglym Bumper Care. Metal ones get sealed/waxed.
I use Griot's Undercarriage Spray on areas that I'm not too particular about (e.g., factory-gooped frame rails of GM trucks).
IME the big thing is to clean stuff up well and then not let it get too dirty again. Cleaning these areas at every wash keeps 'em looking good, and makes it easy to spot leaks/etc. before they get serious.