If I'm totally honest. I don't see this as an investment car at best you're looking at maybe getting MSPR back after mileage is deducted in 10 years if you're lucky. That is assuming it behaves similar to the way the e30 M3 has, which was 34k in 1988. Factor in TVM and the costs of maintenance and you're quickly upside down.
BMW did a great job advertising the car and creating a buzz around it with limited production. The also did a great job of using that buzz and artificial scarcity to hold a high MSRP on the car.
Maybe in 50 or 60 years the car will appreciate but IMHO you're gonna have to hold onto your 1M for a long time to really "profit" from it.