i am the original owner of a 2004 Prius with about 120k miles. I am considering replacing the struts even though they aren't horrible. I figure I won't have the car more than 240k miles so might as well get the struts on earlier rather than later so I enjoy them as long as possible. The only concern is that for the past year or two I have been carrying heavier than spec loads in the hatch (film/video lighting gear) about once a week on average and the suspension occasionally bottoms out. If I keep that up I am worried I will destroy new struts. But I don't really know: Are struts really damaged by heavy loads or is it more the bumps and dynamic forces they encounter that does them in?
Both - its not helpful to strut longevity to carry heavy loads or to drive on bad roads. I assume you have good reason to carry those loads - so just replace the worn suspension parts and don't worry about it.
Heavy duty spring are available for your Prius. I see them advertized for battery kits since adding batterys adds a lot of weight. There are chassis stiffener plates available too.
