Sorry.. I did *NOT* mean to imply that you'd increase power over stock with just a tune up.
I meant.. if your making more power than stock.. I'd choose different parts for the tune up.
IMO if your running a stock engine and a stock tune. The motorcraft parts are a good value.
If your spraying or boosting it.. thats a different story.
As far as aftermarket plugs go.. that seems to be a hotly debated subject around here. Personally I use denso IT20 plugs yr round. But.. that's too support the 75shot of nitrous I use.
He who is enslaved to the compass is free to sail the seas