Dick,
Given the long life of Enya plugs it would have to be a co operative venture among several flyers to get 10 burnt out or marginal plugs. Now R/C is a different matter, especially helis.
I know of many flyers who brag that they have had the same plug in their model for X number of years. Either they don't fly much or that really is some plug that they have in that engine.
Dennis