I have the red and orange leather. The grain on the orange makes it a little grippier, albeit not perfect. I tried using leather conditioner on both, with no change. But I have not tried using alcohol.
I have the Spigen Slim case, it has a matte finish which is easier to grip than the smooth plastic back. I like it, with minimal bulk, and it comes off easily.
Hopefully the stick-on skins for the plastic back will improve the feel, without adding size or making battery changes more difficult.