Hi Nate,
I drove two ML350s one for 5 years as my business car and put many miles on it it was a 2000. The second one was a 2005 and I traded that one after 2 years when a dear hit my car. I checked with MB, BMW and Jaguar for trade in value and since Jaguar gave me the best deal I got a Jaguar AWD.
Now on the first one I considered the factory extended worrenty, however, decided against it and traded for a new one. I know the new MB is no longer as reliable as our Pagoda
then think about it your ML should be okay until you decide to trade in for a new one. The $4500- should cover that time period or you may elect to trade it for a new car for your wife.
Something to think about anyway. In general I don't go for the extended worrenty, seams to me the manufacturers always gain on those deals.
My view anyway, take it with a grain of salt.
Dieter