Why replace them if they still are servicable and work for you? You could always buy a spare set of wheels in case you have to repair the original set, but then you will be trying to find a 5 spd set up etc to keep on the spare unless you just swap over the cassette while the original is being repaired.

It's kind of up to you. I had a spoke break a couple of days ago after approx. 1800+ miles/three months on my "oem" rear wheel (Ritchey hub/Alex rim). When I started researching about broken spokes I came to the decision that there may be more of this in the future so I went and bought two wheelsets/cassettes to "replace" the originals that came on my Fuji. While I am sure that others will say this is wasteful, I say it gives me peace of mind knowing that I won't be down for repair anytime soon. Once I get the original repaired it will serve as my exclusive rear wheel to use on my trainer.

BTW, I only go "down for repair" at the present while I am up here away from home. Once I get back to AZ, and have the space for a home shop etc. I will do all of my own repairs instead of forking out the $ to have someone else do it for me.