It is much simpler than that. The E320 Cab is built on a much more expensive platform than the C-based CLK Cab. The 124 was one of the best built cars in the world and in crash tests performed better than the new 210.
It was much more competitive to develop a C-based Coupe and Cab than from the E-platform.
But; In Auto, Motor & Sport they just revealed a new E-Coupé with four doors(!), it will not be cheap I think. Coming up Dec 04.
Meanwhile we should stick to our well built 124 machines, even the design is coming back in fashion when all the bubble shaped cars disappears. If it wasn´t for the exhaust emission rules we could easely put in good old engines without all the electronics and run them forever...