Buy magnacore's and be done with it.
http://www.magnecor.com/magnecor1/main.htm

 

I don't think wires have any real defined replacement interval. I usually just inspect them, if they are getting dry rotted, leaking, burned, oil soaked, or some other flavor of damage, or resistance gets to high, I replace them. If it's a vehicle that I don't know the history of, (and its mine.....) generally, one of the first things to happen is a complete tuneup......

 

I sure miss the day of 10,000 mile tune ups! Plugs, points, condenser, timimg check & adjustment, distributor cap & rotor, fuel filter, carburettor cleaning and adjustment. Unless you had a modified high performance motor then it was 3000 to 5000 miles.
Damn I miss that!!

 

And lets not forget valve adjustments.

 

Yep! That was fun wasn't it?
Get done and take it for a test drive and when it performed like it should, you felt that you had accomplished something.
No computers involved.
We were mechanics, not technicans.

 

If you keep your wear parts (plugs, cap, rotor) changed out with quality replacements on a reasonable interval you will likely never have a failed coil. Good wires will last the life of the vehicle if taken care of. I change my wear parts based on how much time they have. An hour meter is nice but I just use my gut feel these days. Maybe every two or three oil changes or somewhere there abouts.