I just had my engine shocks replaced on my W126 2 weeks ago, and it does make a considerable difference. The old shocks were all shot and had no dampening effect at all. There used to be a substantial amt of vibration transmitted from the engine to the chassis, especially during idling. After replacing the shocks, the car has become much smoother.
I'm very happy with the results for that amt of money spent. Remember to get the engine shock mounting bushings together with the shocks as well. The rubber bushings would be dried up and distorted and in need of replacement.
1979 W123 (200/M) Midnight Blue
1983 W126 (280SEL) Dupont Deep Black (Previously Pristine Silver)