Not mentioned yet- security, those thieves on the boat will strip cameras, audio systems including speakers, anything that is not required to drive the vehicle off the boat to impound! I was told I was lucky they didn't steal the other seats out of my Volvo! Insurance was a joke.
Don't even think of taking a modified car, car inspections are very strict, I mean even the stock headlight bulbs.
The OP must be loaded ($$$$$) because for the cost of shipping both ways, you could rent a nice BMW for a month.
Get your international driver's license, I don't think they take a stateside license, but you should have it for insurance purposes as well.
If you're thinking of selling the car for a ton of money (or even giving it to family), Germany has high import taxes, designed just for individuals trying to smuggle cars in. "Importstuer"
Another issue, flying in the cheaper rates are usually to London, Paris or Frankfurt; London is closer to a port to pick up a vehicle, no ports at the others mentioned. Cost vs cost, etc.
One last suggestion, get a U.S. Army sticker for the back window, you won't have military tags but it could help keeping the cops away, there is a difference between tourists and military.
Have a great trip!