Agreed...you could go broke replacing everything that is classically suspect on the 300E. Besides, not ALL of the historically-known failures will apply to your car, and subsequently, may not occur at any particular mileage.
Most of the problems are due to heat and age factors, and service history, use/abuse of driver, exposure to elements (sun rain snow, etc.) in a particular geographical area all attribute to the wear pattern on your vehicle.
So enjoy your vehicle, maintain fluids, and fix/replace as you go. Otherwise, you could get pretty neurotic just thinking about when the next inevitable repair will occur.
Fortunately, parts for this model aren't particularly expensive, and most repairs are do-it-yourself with a modest set of hand tools.
Get a hold of a repair CD or a good shop manual, and you will be pleased at how much you can tackle on your own.
Most of all, buy the parts you need at FastLane...terrific prices, reasonable shipping, and a great supply of OEM replacement parts!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car