Originally Posted by
globie
What should I be looking for to know when it's time to change them out?
The pavement rushing up to meet your face.
Sorry couldn't help my self.
Keep a close eye on the brake track, put a straight edge on it and check to see how concave it is. It's probably pretty close to retirement. Google 'worn rims', and look at the images.
Is there a shop that sell used bikes near you? They may have some better wheels you could buy