Personally I think the matt grey finish on the lower spec models in the UK looks way better than the glossy black. I might be totally wrong but I think it might be the other way around in the rest of Europe. Higher specs get the matt grey and lower spec gets the cheap looking glossy black.
I had piano black in my Corsa D and it didn't stratch, it was fine. I put a scratch in it myself accidentally when I was removing the radio but otherwise it was fine. Hoping the Astra uses the same material!