This is simply cosmetic damage that could be rectified by an alloy wheel refurbisher. Because BMW had voluntarily offered to replace the wheels I don't think you could successfully use the Small Claims Track of the County Court to sue for the cost of the wheels or of the refurbishment.

If you get them refurbished it is always better to have the wheels painted or powder coated and then lacquered with heat resistant paint. Polished alloy that is simply lacquered is always vulnerable to stone chipping and electrolytic corrosion under the lacquer.