[MTI]

Bosch coppers have worked fine for me, so I never felt the need to change. They're cheap,...

Bosch coppers have worked fine for me, so I never felt the need to change. They're cheap, easy to gap. My understanding is that the platinum plugs work fine in our cars, but the main selling point on them is that they can stay in longer, which may not be a good thing on older engines with alloy heads. I've heard that the 4 prong'd plugs are a pain to set the gap.

 

[Bruce R.]

I spoke on the phone with an NGK rep. His comments were.....

He used GM as a reference, so take that for what it's worth.
If the "normal" lifespan of standard plugs is between 10K and 30K miles, Platinum plugs can run up to ~ 100K miles, and Iridium plugs will go up to ~ 180K miles. There is no apparent down side to either of these plugs other then cost, and a few benefits including slightly better gas mileage.
If we can run almost 200K miles on a set of plugs, few Mercedes cars will ever need more then 4 sets between overhauls.