I would first like to point out that although I hate to see S/S wetsanded or coarsely buffed a lot, I know for a fact that many people still do it. I would venture to guess that they really don't understand the cause & effect of those actions (till later on afterwards), or they do and it's still the lesser of evils because they need to remove some bad issues in the paint. I can't say whether it's right or wrong in every case, but only that people should know and understand the technical side and it's possible consequences. Let's face it- paint will fade even if you do NOTHING, from exposure to the sun etc. So eventually, you're GOING to have to polish it to some degree.
As for your Volvo, consider yourself lucky, but i'll bet you keep wax or sealant on it too, being a learned Autopian and all. I guess it's going to have variables as with anything, and paint manufacturer and type of paint (even color) used come into play, as well as film build. I know i've read where S/S (acrylic) enamel systems years ago were 10-12 MILs thick, compared to (at most ) 2 MILS of clearcoat on oem paint, so although there's more "headroom" there to buff on older S/S paint (% wise) you will eventually get to that "slippery slope"as you so well put it, IF you keep having to go real aggressive. Todays recent oem S/S urethanes (the Lexus' black onyx for example) are about 2 MILS, the same as their base/clear counterparts. In essence, they are the same paint, one is just non-pigmented.
What is happening with the dieback/dulling in most cases (the case in one thread of wetsanding deeply notwithstanding - that was severe resin removal in one fell swoop) is whenever you polish paint, you're breaking the surface tension and allowing solvent release. The solvents are part of the resin system, in essence they give health to the resins that produce the shine. This is ok and part of the deal to a certain ("slippery slope" ) extent, except that S/S suffers more than base/clear because the pigment is part of the resin system / solvent content. You're good for a few years with this process generally, the removing of oxidized paint...then when that "glossy" resin layer are depleted via abrasives ...yep.
Even some body shops will do it(sand/compound), because their primary interest is in returning a customer's car in the best possible finish, and they often need to sand out debris and orange peel. Are they doing their customer's a disservice? That's one way to look at it if enough paint is removed, because it shortens the life expectancy of the finish, as well as the amount of upkeep the paint will need. But they are thinking short term in their own interests.
I recall a number of painters saying these things over at autobodypro forums in the past (even to other pros that didn't address it), and that they learned the hard way too. As time goes on, less and less cars will have S/S paint, aside from an inexpensive repaint choice, so for the consumer in general, it won't be an issue they need to be concerned with.
As you may know...
Lacquers are very high solvent content paints to begin with, and since they are air cured and UN-catalyzed, they will be forever off gassing and drying, so they suffer dieback whenever their surface tension is broken. They will dull even right after being sprayed because of these things. But they shine up easily and well too, albiet on a regularly needy basis.
I don't think you'd find lacquer on anything much outside of a classic show car these days.
Not an "expert" on this, but I sure have learned a lot from some people in the biz over the years. Hope this helps.
) has me wondering...slippery slopes and all.
It sure looks and behaves like lacquer! Heh heh, I just can't think of cars that are younger than I am as "classics" quite yet.