Is there an avg time they say to change them? I'm putting new wires in and was going to change them, but it's over $45 for the cap. There are no problems with it now. I'll most likely check it after the new plugs and wires are in.
I always change the wires, plugs, cap and rotor as a part of a tune up. Since you are already taking the stuff off, its worth the 45 bucks in my opinion!