What does a healthy cast iron skillet look like? I've read plenty about how to restore and season cast iron, but I have no clue whether any of the old cast iron I've inherited could benefit from this.

Is healthy cast iron black? or should it be somewhat metallic looking (ie. a bit silvery, like steel). Does the black color come from even one seasoning process, or will it develop over time?

Is is smooth? or is it alright if there are some lumps in it's surface texture?

and finally: after seasoning, is the surface supposed to have a slight oily appearance or should it be totally dry? and will healthy cast iron leave a residue on a rag if I wipe it? Some of mine do, and I'm not sure if that is good or bad.
Ideally it should be matte to just-slightly-shiny black and very smooth. This article has some terrific information on the ideal oil to use (flaxseed) and method for seasoning, with actual scientific grounding.