I agree with you that replacing the entire cooling system is probably a good way to go as it sure does seem replacing one part causes another to fail right after. Myself though, I would probably wait for the first part to go, then replace the whole system. Not just do it based on a mileage recommendation. The system in my e36 was overhauled, but that was at over 200,000 miles. I would have wasted a ton of money if I just decided to do it at 100,000 intervals regardless of failure.

At the end of the day you can replace all of these typical items and still end up stranded on the side of the road. Might as well go ahead and change your brake calipers, ignition coils, ecu, shock mounts, wheel bearings, etc. Where does it end? It is a machine and regardless of how hard core you are with regards to maintenance, something is going to break.

I view changing plugs two or three times as often as recommended as changing light bulbs before they burn out because both are a waste of money. My plugs have been in for 120,000 miles and the car runs as smooth as can be with plenty of power. Unless there is another underlying issue such as oil leaking into the plug holes, leaving your plugs in for the full 100,000 mile interval is not going to leave you stranded on the side of the road. I haven't heard of anyone who was left stranded because they followed the manufacturers recommendation for spark plug intervals.

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Profeshenal spellar