Most of today's vehicles modern BC/CC paint systems have a total thickness, of all the paint films, in the range of 4.5-6.0 mils (114-152 microns; or, .0045-.006 inches)
The CC thickness generally is in the 2 mils range (50 microns; or, .002 inches ).
Depending on the OEM, it is recommended to not remove more than 25% of the CC paint film...between .3-.5 mils (about 7.5-12.5 microns; or, .0003-.0005 inches.
Hard to detect/measure with the "naked-eye"!!!
One of the more accurate ways to measure these tiny, fractional amounts would be in using a measurement tool...an EPTG...that measures up to three individual "layers" of 'films'/coatings...Such as the DeFelsko PosiTector 200 b/advanced series.
There should be a base measurement, a snap-shot if you will, when the vehicles are new (having an "un-aged" CC). Or, before any more abrasion from any source can take place, a current real-time measurement of the CC (an "aged" CC) This measurement can be compared to what is considered 'the norm'. This and other styles of EPTG's are usually thought to be cost-prohibitive tools, though.
Other than that, more affordable, but less accurate measurements are obtained by the methods you prescribe to using...More or less hoping that so far, and hoping to never, remove too much CC.
That, and/or real-world, over time, and on many varied vehicles..."Abrading the CC" experience.
{Still just guessing, wishing & hoping scenarios without an EPTG, IMO.}
Wolfgang Finishing Glaze, although being described as having the ability of removing 2500 grit swirl marks using a DA and finishing pads, can also be used via hand application as well.
Because your vehicle is, (according to how I interpret its usage), a Semi-Garage Queen, what I would do is:
Just employ a spot-polishing method (either by machine/hand) with this Wolfgang, or similar product, to remove any of the
marring deemed necessary...Not the entire vehicle every time.
After the above step, and if overly concerned/worried about the reduction of the CC's thickness:
I'd use this Wolfgang or similar products like 3M Imperial Hand Glaze, via hand application, over the entire vehicle's CC paint surfaces between 2-4 times yearly, or more if so desired, without having any of the "removing too much CC" concerns.....
Always followed by an application of a protective LSP, (In my case...preferably a sealant)....Unless one of the new coatings has appeal to you.
Sorry to hear you get
marring from washing and LSPing your vehicle, even with using, as you say: Careful methods.
IMO...The need, then, for basically: "how many abrasive-polishing-sessions" to remove such marring may be performed; and, your concern for "prevention methods" to further preserve your vehicle's CC thickness, would be less of a prominent issue for you.
No matter what the reason(s)....
I rank the consideration of CC's preservation/protection as a very important, prominent topic.
Bob