Stephen, thank you for your very scientific observations, and professional opinions. It's good to get something of a definitive argument on this 'hot potato' of a subject.
I have to say, that I go entirely for looks in this case, and have been converted by the idea that in the process of any stripping, the horn usually gets a 'tune-up' job anyway, so it's bound to sound different. If it falls apart.. hey ho, so be it.
In fact, to finally lay a lot of this to rest (in my mind at least) I have gone out and bought a fully painted horn (!). So far, from my tests (side by side) there is no difference (using the same mouthpiece) as the stripped horn. Certainly in terms of 'significant' differences, only what you might expect from two horns side by side. The heavily painted one does not sound 'muffled', 'dead', nor 'lifeless'. If anything, it's slightly brighter!...
The sound issue of de-lacquering is a moot point. I am not convinced.