I'm assuming the lower front ride height is the result of sagging springs. While higher spring pads may restore the ride height, bear in mind that the springs will still be shorter than normal, and will not offer you a full range of travel, particularly under compression. Age, use and possibly corrosion has caused the spring (compression) rates to change. Handling and ride will not return to Mercedes specs simply by the addition of the pads.
Other than under heavy braking, I can't see how a difference in front vs. rear ride height would have any material effect on dynamic weight distribution. Obviously, static weight distribution would not be affected.
Another matter to consider: Like most modern cars, the front suspension is designed to allow the wheels to move slightly rearward when the front suspension is under compression. This rearward motion allows the suspension to absorb some of the shock of hitting a road defect (pothole). If the chassis of your car is not perfectly parallel to the road surface (as it would not be in the event of sagging front springs)the wheels would move in a more vertical plane than intended under suspension compression, with loss of this shock absorbing ability. There goes the ride.
As an aside, other elements of the front suspension geometry (caster, camber)would be affected, causing a decline in handling abilities. If my preceding thoughts are less than clear, imagine this: an entire front subframe and front suspension (absent the rest of the car) moving down the road at speed, reacting to bumps and corners as designed. Now imagine tilting the subframe, and therefore the front suspension, forward a few degrees. Think the suspension will still perform optimally? Not a chance.
This is my long-winded way of concurring with your idea to restore front ride height, but not by rubber pads, by buying 4 new springs.