The E9X M3 was a far better car in every respect than the previous generation Cayman.
The new one looks awesome.
However E9X M3 TCO should be far lower (unless you are the type that pays cash for your car). When I was shopping (before I bought my current 2011) I got a quote on a Cayman S. Even with a substantial discount on the Cayman, my M3 has been approximately 1/3 the cost of the Cayman. Don't forget to compare both cars and the financing/lease deals offered by both companies. BMWFS practically gives the M3 away when you compare against other makes..