Taking pictures before install is a smart idea to prove it's not covering damage. Cliff makes some great protectors that can prevent damage and I see no reason why they would decrease the value of a pin. Cliff has given a lot to the community and it's good to know guys like him are around finding ways to help other pinheads out.

And to the best of my knowledge there is no Cliffy protector that you need to glue on they are all removable via screws already in place.