I just received a sony 7506 today, boy it is packed like a dream! Silk, black, gold...
The output is hot and I can hear all the noise the canon a1 produces in the headphone amp. But over here the sony is 2x expensive, you can also buy a good beyerdynamic I think. (DT 250/250 Ohm)
Same exact headphone as the 7506, except from an earlier line and without the gold plated plug. Half the price. Don't believe me? Ask around at Head-Fi.
Yes. Or more generally, extra resistance to oxidation.
However, I've used pairs of V6's (with no gold plating) that have been completely beat to hell and driven into the dirt, and I haven't yet run into one that has a bad connection due to an oxidized plug.