Originally Posted by Big AL
If your car doesn't bounce and you're not experiencing any abnormal tire wear such as cupping then why change them? Maybe your car was driven mainly on decent roads which would keep your struts/shocks from wearing out sooner.
Struts go really slowly over time and it's very difficult to tell "good" from "bad" if you drive your car a lot. The first time I changed mine I was shocked at how much better the ride became. 173k miles is past the point where most struts are effective.