The crank position sensors do wear out and can leave you stranded on the side of the road. If yours is the original, it is probably on its last legs. If you plan on driving this car for a while you should replace it. It is a very easy DIY. I think you can find them for around $80 (American).
I just replaced my spark plugs at about 67,000 miles. Your car's mileage is about the same. After removing them I could see that they were noticeably worn. IMHO, the recommended 100,000 mile interval is too much. There is also the issue of damaging the threads in the aluminum head if the plugs are left in for too long. The spark plugs have been in your car about 7 years so it would be prudent to replace them even if they are not causing the problems you described. If you decide to replace the spark plugs yourself, do lots of reading in this forum for cautions and tips (EX: Don't listen to anyone that tells you it is OK to use resistor plugs in this car. OEM plugs are non-resistor, replace with like).
Good Luck, Dan

__________________
2012 E350 Bluetech