The point he was trying to make probably came off the wrong way.
What he was saying is that if you are experiencing an improvement, it is because the old components were slightly worn out. Even if your old plugs don't look that bad, their resistance and gap slowly change with use in ways that are not obvious to the naked eye. Coils are the same way, and just swapping components means taking harnesses or wires off that might have built up a small amount of corrosion or resistance between them, and that gets scraped off when the wires are moved.
Anyway, the point that he was trying to make is that those things are no better than the parts they replaced if the parts they replaced were new. Aftermarket coils don't perform any better than OEM ones, and the same can be said with plugs. All any of those things are going to do is ignite your gasoline in your combustion chamber. They expose a combustible mix of fuel to an electrical current that is of a high enough voltage to arc a gap on a plug, and thus create plasma in the gap. This plasma heats the fuel mixture around itself causing combustion. Any energy beyond what is required to heat the mixture the arc comes into contact with beyond the point of ignition is wasted, therefore, even if those components did make more, it would be a waste unless you could set your gap on your plugs much larger than OEM, which you didn't. Even if you did, you would only be talking about a few thousandths of an inch, and you are still in a zero sum game, since the electricity used to ignite the fuel comes from the engine running... High power ignition and such is only really going to help on vehicles that run very high RPMs and very high compression or aggressive ignition and valve timing, things that make combustion difficult. On a daily driver, you will never see a difference outside of a few tenths or hundredths of a horsepower, and the air temperature or a billion RANDOM variables can have more of an effect than that.
In short, it is good to buy quality parts to replace old ones, but what he was getting at was not to fall into the trap of buying replacements just because they are aftermarket and have some slick advertising. You need to spend the money on good parts, but don't bother buying the more expensive stuff just because it says it can do it better than the OEM replacement. Making cars faster or better isn't just about buying the fanciest stuff, it is about intelligent tuning and engineering. Beyond that, the most anything else is going to provide is a placebo effect. Always remember, the more horsepower your butt-dyno thinks your engine is making is inversely proportional to how heavy or full your wallet is.
Dunno about you; but I hear voices in my head & they tell me to do things like buy only aftermarket stuff............
