It depends on the mod. Some mods are easily an improvement; new tires are probably a good example here, because automakers frequently install crappy tires at the factory because of some sort of deal with the tire company, and worse, replacement for that same model of tire end up being much more expensive than better tires in the same size, probably because many consumers mistakenly think they need the exact same tire.
But yeah, most "enthusiast" mods are a waste of money and make the vehicle worse.
But yeah, most "enthusiast" mods are a waste of money and make the vehicle worse.