<grin> No not any more Bob I was only joking. I did have and old Ford Prefect (obligatory moss green) eons ago. Nowdays I drive an old (1993) american Chrysler convertible called a LeBaron.
As you know, I'm no expert and open to be corrected, but all bar one 'old' sax I have ever seen (laquer or plate) has shown the signs of wear... and so they should, thinks I. Most of this 'wear' that I've noticed appears to 'me' to be either high use area's (as you say keys etc) or the parts that past owners have 'polished' a lot.
I don't know about your cloth, but the ones that came with my Hanson's were just plain old microfibre (non abrasive) and a quick wipe over with these did not cause any 'black' to come off.
However, all the proprietry silver cloths and polishes, even those that said they were non-abrasive caused the 'black on the cloth' problem. I was always under the impression that any residue coming off on a cloth was a sign that silver was being removed, so I went the pure polish route, first Pledge and now, as mentioned, Carnuba wax (can be bought as 'Mothers' car wax). It works very well "for me".
I gotta admit, I do tend to be a boring old polishing addict, mainly because the horns are relatively new, but I do agree with mfox that a 'players' (I'm not in that class 🙁 ) horn looks nice 'el naturale'.
Having looked at the pics in the past of your Dolly and how good it is, I think I would be inclinded to keep it clean by perhaps going over it once with a light silver polish and after that 'Carnuba' when it gets dirty.
ONLY M(Humble)O.
BTW: my ole' lady is mad keen on Native American jewellery (silver and torquise) and her jeweller suggested that she use a cloth that doesn't take off any black (even on solid silver) and gave her some small sheet of anti-oxidizing paper to put in her jewellery box. I 'think' something similar is available in larger sizes which is suitable for putting in sax cases.
Now talking of old Ford Prefects... whatever happened to the headlight dip switches that used to be on the floor (foot operated)... darn I miss those :S
Saludos,
Ken.