| i had some mesh stone guards on my previous mini 'cos like you i liked the look. i think the ones i got were stainless though so they didn't rust up. i've always waxed any chrome metal items for the reasons you mention. when i used to work in a factory that included a plating shop most of the guys who wanted bike & car parts chroming actually went for nickel instead as it isn't as porous as chrome & it could be made just as shiny.
most of the chrome items on the mini (headlamp surrounds, grille etc) are plastic coated, not metal so there's no way they're going to rust but water can get under poorly coated parts causing the chrome finish to bubble. i had this recently on my tailgate handle & the dealer swapped it for a new one at service | 
