More or less, they're good till they're not. You can absolutely change them as preventative, and I've done that on other vehicles (my wifes commuter, she was doing 500 miles a week through BFE Wyoming, half on Monday and half on Friday ~ I didn't want her to have issues). Just depends on your level of risk tolerance.

I'll probably replace mine before they fail as I go in and do the rear seals (there's a little goo in the ABS area) and when I put manual hubs on the front (fuel economy, because I want to) just as a course of addressing age, known failure points and doing mods. But I don't worry about them. I remember driving a car on a road-trip where one went out over 600 miles from home. Howled the whole way home, which was annoying, but it never felt unsafe.