No you are literally paying £50 for a better shell/better looking card. I don't even know if the plastic version was intended from the beginning, because they showed the silver one first. I think they basically realised that this huge die + HBM2 + nice looking cooler was going to be $ so they came up with the plastic version instead.
It's quite cheeky really. You can buy a plastic one for $500, which is the same price as the 1080, or you can pay $50 more if you want it to look better. I just hope AMD have left some legs in it, because I can see the 1080 dropping pretty damn soon. Well, it already has, but only to £449.