I think unless one of the shocks or struts breaks or leaks it is like getting eyeglasses. You'll know when you need 'em, cause the car won't do things it used to do.

I've replaced shocks once or twice on previous cars when a shop tech suggested they were "worn" (where I myself had not suspected any problem) and was disappointed to find out I couldn't tell the difference between old and new.

I also think ride and handling quality depends on the combination of shocks/struts, tires (and their inflation), and the suspension design, all working together (or against one another). So changing one item may or may not make a big difference. My personal experience is that changing to a different brand or better grade of tire has had the most noticeable effects on overall driving satisfaction.