Bart, I think MSD recommends against copper leads because they want to avoid electromagnetic interference (EMI). This is not about avoiding ignition noise in your radio, but about making sure your fine MSD ignition module doesn't get "confused" by EMI signals feeding back into the electronics.
MSD modules look great, but I personally find the original Murena electronic igntion system perfectly capable and well performing. The igniton problems I have seen have been due to bad coils and fouled plugs. Some have reported defective ignition modules, so I keep a spare. I've got a box full of fresh NGK plugs and a set in the car so I can replace them when needed.
Why carbon, you ask? EMI is the reason. You don't want noise in the system as that can mess everything up. Further, the resistance in the conductor doesn't matter with the high voltages you're running on the coil. Will an EMI resistor do the same? I honestly don't know, but why bother? - good quality carbon leads last long and work great
/Anders