I never saw the point of skins. Unless its camo or wildlife. neuroanatomist said it vary well.
But just lately I herd a photographer talking about them and why you should buy them.
I think it was Moose Peterson. He said, when you want to sell them because of upgrade or other reasons. You take the lens skin off and it looks brand new under it, and you can sell it for more, and get more money back then you would with out it, the lens looking more well used.
He has a point, but I still wouldn't buy them. Its money I could spend on other thing or putting towards a new lens, body, Starbucks, etc. If or when i sell a lens, it would because of a upgrade to a L lens, my none L lens will never have the life span of a L lens cause they will get replaced with a L lens, sooner then the life span of a L lens.