Typically these wires are attached to the distributor cap and needs to be changed when you are having a "hard" start. The wires should be fine but the distributor cap usually goes south, with corrosion of the contacts. Sometimes the corrosion can be cleaned (sanding) but will eventually go "bad" again. Service stations would like to get your business, so naturally they would advise a more frequent change.
I would say, if you are getting a normal start and no problems with losing power whilst driving you are good to go. Once you start noticing a difficulty with starting and loss of power whilst driving, then you will need to change the wires.