It is fairly rare, or at least it was until the duplicating started. It is worth whatever you can get for it and you are lucky to get it because so far I have got it once and got a matte paint the other eleven times.
Just so you know, when you get a special paint awarded (usually matte) for every 30 cars in your garage, if it's not one that you want don't press OK and quit/restart the game until it gives up the one you do want (this includes chrome).
I can't rmb exactly, it was quite early, when I was more after the cars than paints... I got lucky, I didn't even know I got it until my friend told me that there's such colour.
or just do what Ya Pops said, before the time you hit multiples of 30 cars, saved and back up the game, buy or redeem your 30th car... see if you got the silver chrome, if not reload until you got what you like.
