I asked the question when I bought my car here, in the Czech Republic (someday I expect to move back the US, and I wanted to know I could bring the car with me if I bought it here). I was told the US and Euro-spec cars are essentially identical. The major diff. is floating roaters in Europe vs. fixed in the US. I am not sure that you will have to change them and, if so, what this would cost (since the brakes get mixed reviews, it might be a reason to upgrade if you had to make a change). The dealer also thought the blinkers might be different. Again, I don't know if they would need to be changed. But, all major components are the same, and the Euro car should be 50 state legal. I was told it is a lot of paperwork, and you need the cooperation of the dealer in Europe from which you buy the car (my dealer promised they would help if and when the time comes). You would likely want a good customs broker on the US end to assist. I doubt you could buy direct from BMW in Germany. They probably would not want to do it if they knew you were going to do an end run around BMW NA's dealer network. And, I was told the selling dealer needs to assist to get the car into the US (I don't know why you can't just take delivery and drive it to a shipping company, but that's what I've been told).
FYI, I ordered my car in late Nov. and took delivery Feb. 1. My dealer could have had it in 8 weeks, but I wanted to be sure I got an '00 final build date. I got every option available, and paid around $95K. With the strength of the US$, it would probably be $88K now. That includes a 25% VAT, which you get back if you export the car out of the country within 60 days of delivery. So, when you do the math, it is a good price (after return of the VAT). I, of course, do not get VAT back, but them's the breaks.
It's not a bad plan, but you will have to do a lot of leg work.