IMHO, if you have an idle problem with the plugs gapped at the recommended gap, it isn't the plugs.

As for the wires, I happened to damage one plug wire trying to get it off a '91 300E with only 50K on the clock. I ordered a new set from MB dealer Caliber and installed them. Apparently there were more problems than just that one wire. The new wires made a noticible improvement in fuel mileage despite no indication that I had any problems before changing them.

I recommend using Bosch original equipment wires no matter where you get them.

I've also said this before, get yourself a can of HD silicon spray and spray the insides of the boots of the plug wires and they will come off much easier. It also prevents inadvertant damage to the wires trying to get them off the plugs with anything other than the correct plug pliers.

I paid $134 for the MB wires from Caliber.