I have read this thread and it seems no one actually narrowed down the problem of too much resistence in the ignition system. Any one who has ever used a lab scope on the ignition knows you look at the primary side of the coil and get a good indication of what is going on in the secondary. Bad plug wires, rotors, fouled plugs, etc are clearly displayed. This is the results of the secondary inducing a signal back into the primary. If the resistance is low (fouled plug) the secondary voltage will be low. If the resistance is to high (open wire) the secondary voltage will be very high. Since this voltage is induced back into the primary, the ignition moduel sees this induced voltage also. This is what gets the moduels. Is adding a resistor plug enough resistance to make the voltage go high enough to damage the moduel? I don't know. I didn't design it. I do know, always use what the designers say to use.
When I first got my 500SEL, it had been used as a parts car and many things were missing. One thing was the ign moduel. I had on hand an MSD ignition moduel and used it to save a little money until iI knew of I could get the car running and it ran great. The first time I replaced the plugs, I ordered NGK plugs for an 84 500 SEL and I got resistor plugs(BP5RES). The engine started missing at idle. I found some NGK plugs with out resistor(BP5ES), installed them and the engine was again smooth as silk. On a bet I put a set of Bosch Plat plugs in and performance went down hill from the start. I took the car to the dude that make the bet with me. He drove the car, we reinstalled the used BP5ES plugs back in and the car ran smooth as silk again. Easyest $100 I ever made. Now all of this was with the MSD ignition which is capable of jumping about 3/4 inch with multible sparks/firing. So the above tells me that something about the resistor plugs makes a difference and the plat plugs are useless in our engins.
The above are my obsavations, your mileage may vary.

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84 500 SEL (307,xxx miles)