Strangely enough, Paul, I feel the same way about my stock plugs.....
but it always SEEMS that ANY bike benefits from fresh plugs, no matter how well it ran before.
My problem is with OEM versus replacement plugs. An AC Delco rep recently told me a little story about how the stock plugs that go into GM engines are of a FAR better quality than the AC's you can buy at Cambodian Tire or the other mass market stores. I thought about this and wondered if it made economic sense for AC to run 2 plug assembly lines. I'm sure AC's accountants know to the 1/10 of a cent if it makes sense or not. I'm also sure that if this IS true, then NGK will be doing the same thing.
It would be nice to get verification of this "urban myth" ???
If it IS true that there are two "qualities" of plugs, then a guy would be crazy to bin the stock plugs without reason.
OTOH, if the myth is NOT true, then a guy can change plugs with no worries.
Sometimes I wonder if I worry about (mostly) inconsequential things too much.....although spark plugs are not exactly inconsequentia itemsl, IMO.