Again, to your question..NO, the value will not be affected other than that whatever you put into making it the color you want will likely be "eaten" by you should you want to sell in the future. It won't make it less valuable, but it won't make it more valuable either. Why a CSX Cobra was ever painted "Diamond" black in the first place is sort of a head scratcher to me. Not a very period type of finish.
I also have owned various black cars including a black ERA Cobra and I presently own a black Shelby GT-H. There is black car maintenance and then there is an entirely other league of black car maintenance. If you elect for a top show quality black paint job with perfect body work underneath and a proper cut/buff finish it is 10 times harder to maintain than a factory type of black car. I know, because I'm living it right now. I had my Shelby repainted as I wanted as close to a perfect car as I could get. It is very difficult work to keep it swirl free. A perfectly flat finish reveals every single thing that a finish with a little orange peel can more easily hide.
I really enjoyed my black ERA, and because of the many curves to the body and relatively small amount of painted surface (compared to a full size car) it wasn't that bad. It took me half the time or less to machine polish it compared to my Shelby and it looked fantastic. If you want a black car, go for it. Just know you have choices about how far to take things.
