It seems we can't get away from that question so I figured I'd put in my 1 cent/penny.
Whether to clean a coin or not depends totally on the dirty coin in question. If it's not a key date nor worth a lot and if the coin is ugly because of the crud that's on it, then what harm can there be from making it look better, as long as you don't go overboard?
I picked up a Connecticut Copper that was in a NCS slab and it was still dirty after they "conserved" it.
I couldn't take the dirt so I cleaned it.
You can look at the before and after pics and draw your own conclusion as to which looks better and which you'd prefer, if it was your coin.
This is actually a coin that's worth quite a bit, since it's a 33.4-q (R-5) but like I said in the beginning, I couldn't take the dirt on the coin so I had to remove it.
Feel free to show before-and-after pics of your cleaning experiments.
Ribbit
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