When you sell stuff you have to factor in the fact that you owned it for a period of time. I've sold lots of things at half the price I paid for them. Consider that I owned them for 20+ years I got my moneys worth IMO.
To the original "should I keep or sell RailKing?" all depends on you. Railking that is scale or close to it offers plenty of value to me. One that is not scale at all I would sell. But that's my way of looking at it.