My DH builds models...and he's also scratch-built stuff, too. He did an Enterprise that came from a kit...but he scratch-built the finer details and re-shaped the hull and stuff like that.
Mostly he builds aircraft from kits...he built me a 1/48 scale P-38 Lightning that is just gorgeous.
Back to the subject..there is a magazine called "Fine Scale Modeler" that we get and one of their main complaints is how such a loss of detail occurs when the item goes from artist's rendition to retail kit. DH buys a lot of resin model "correction" parts for the kits he buys retail! There are lots and lots of people out there, in their garages, making resin molded parts for commercial modeling kits.