Investments or Waste of Money?

To keep the car a bit longer than usual, do I replace parts before they really go bad, or should these parts be replaced where the maximum benefit can be realized?

For most of us, the suspension parts, like shocks and struts are not replaced until they are already completely out of service life, and caused some damage to the tires and steering. If the struts are good for 80-150k miles, and only planning to keep the vehicle for 200~220K, should they be replaced half-way, regardless whether struts/shocks are completely out of commission?

Well, I did it. My cars has new struts/shocks and oxygen sensors replaced - even though the handling was still acceptable, the check-engine light wasn't on yet. Replacing these parts on my own terms, and replacing them at my half-way mark of planned ownership, I hope this was a logical decisions.

The new suspension parts improves the "braking" more secure, there is no hint of nose dive anymore. I am going the turn at the usual high-speed, the cars doesn't lean and slide any more. It handles like a real new fun car all over again.