Definately leave as is, chrome looks great on a Cooper.
Tigger.
Hold it, not so fast. I've just looked at the photos in your gallery and it's not so obvious. You need to either add more chrome elsewhere (side vents, Cooper S filler cap etc) to balance the chrome out a bit, or make the centre of the grill black as you suggest.
As to which to do don't ask me, I'm a chromaholic, so you won't get any unbiased advice from me
Tigger.