The impacts of well thought out mods are real. Most mass produced products are under optimized to meet price targets, fleet emissions standards, and average consumer needs. The vast majority of folks a good with that. Some people need more.
My VROD has modified exhaust, intake, and EFI fuel maps that completely change the personality of the bike. It functions far more efficiently. Many of the enhancements made by users were adopted into subsequent model year designs.
Last night I was at Cruising the Gut in Vancouver and there were several hundred folks celebrating their modifications.
Personalization is fun too, but the performance mods can far exceed OEM limitations.