Yeah, I thought mine were ok too... no noises, car tracked normally, etc etc. But the dust boots were totally shot and it would only be a matter of time before the joint started to fail and make noise. It is very hard to visually inspect these bushings. After 15 years / 150kmi, I'd replace them on principle, even if there are no obvious symptoms. They're cheap, and not difficult to R&R.
Side note: Omegabenz claims that if worn, these bushings can cause up to 1 degree of excess negative camber in the rear, which will wear the inside of the rear tires. I don't have a way to confirm this but I also don't doubt that he's right!
