I just upgraded from a Black 3DS to a Black 3DS XL with MH3, was definitely worth it in my opinion. I prefer everything about the XL now that I've used it. More comfortable to hold, better material, everything really. My transfer went nice and smoothly as well, so everything is now on my XL
I'm really surprised the all Black 3DS XL isn't out over there, then again I was shocked when it didn't even exist when the 3DS XL was announced. I really don't like many of the coloured ones that much.