Yes that 600 MB Pullman is a real trophy. As for our President riding in it, well that day is now long gone. The car is not bullet, bomb, missile or anything proof and the last thing I want to see is for that car to be blown up.
The German Chancellor is at minimal risk of an assasination attempt, as is King Abdullah of Jordan who still uses his late father's (King Hussein) '64 Lincoln Continental convertible for state occasions. It was also used for his wedding and coronation:

In addition to being armoured to the core, the MB Limo that is in use by the President now probably has such creature comforts within, that it would probably shadow the MB 600 in comparison. It would be good as a show car but to be kept in running condition.