I find that dark colors tend to show less wear - or at least you can camouflage scratches better. I have both the red and black smart cases. If I scratch the red one, I'll rub leather conditioner to the scratch specifically and then to the whole case and consider anything left as patina. Scratches on the black case can covered with shoe polish if needed and then rubbed with the conditioner.
I know how you feel though - wanting to keep the case nice for as long as possible. In addition to the conditioner, I also sprayed both of my cases with leather protector as I'm more concerned with staining especially with the red one.