I have about 10 flyable planes. I have never had a deadstick due to a bad plug. I don't change them on a regular basis either. The first sign of a bad plug is usually that the engine won't idle properly. If that happens change your plug. A couple of times I have had a flight, landed and shutdown normally. Next time I go to fly the engine won't start, turns out the plug is dead. Don't get to worried about a plug causing a deadstick. It does not happen often and usually you will get some signs of a dying plug.
P.S. If a newish plug fails it is usually because it has been run lean.