Another advantage of a coupe is the increased visibility you get out the side windows due to the lack of a door post between the front and back windows. This makes it a little easier to check your blindspots on the freeway. It took me a little while to get used to decreased visibility in the 300SD.
The main disadvantage that I can think of is the obvious one: the coupe only has 2 doors. The coupe might also be more of a "cop magnet," but my experience has been that Mercedes in general are not cop magnets at all. <knocking on wood>
I'd weigh the coupe's nicer looks (if you find the coupe a more attractive car) against its higher price and base my decision on that. Keep in mind the coupe will be worth more if you sell it too. Either way you'll have a lot nicer car than an Acura.
Santa Barbara, CA