As you probably know KOP, black cars are notorious for showing up the dirt so I think getting a protective coating is a good idea if it helps it stay clean as well as make it easier to clean. It really depends of what sort of owner you are, will you be the type to be happy cleaning it every weekend or less or eventually resent doing it? I personally wouldn't buy a black car for that very reason as I've only ever cleaned mine when I really have to in thirty years of ownership irrespective of it's age or condtion but then it still looks presentable at a distance even when it is actually quite filthy.
Interweb pic of my model, it's a fairly bright blue so hides the dirt fairly easily.