It's the most reasonable choice. As you are not in France, I believe status thresholds are quite low at 40000 miles and you may even be able to make Rouge if you do 3-4 trips from Germany to secondary US airports via Paris via JFK or some other US gateway. KL, CO and NW will join Skyteam in September. I believe you can earn miles for EVERY flight for which you've bought a Skyteam-coded ticket.
I know nothing about Amtrak therefore unable to help you with that.
Redemption only makes good financial sense if you are patient enough to wait till you have enough miles to get a longhaul Biz or First class ticket.