I agree, this is a tough one - however, I would say...
1. Many people find the M3CS to be priced excessively for what you get.
2. There are some still available (car is not that hot)
So in terms of value and rarity, it doesn't have either - yet, it is one of the more expensive M3s you can buy.
Therefore, I believe, that based on past history, it will depreciate at a higher percentage of purchase price than a lower optioned standard M3.
Alas, as the famous ASIA song goes..."Only Time Will Tell"
