This could be a solution for hard to find and custom parts for LH Cars. 3D scanning apps are starting to show up for the I Phone and Android phones and Maker Spaces are starting appear around the country so access to 3D printers is getting easier.
Definitely a possible market; I would wonder about the quality of the "print" plastic, etc, and how it would hold up compared to injection molding.
I've got a friend in California that has made up a couple car parts on his 3D printer, a hub cap, and a little door link piece for an old Volkswagen that couldnt be found anymore. Both seem to be holding up according to him.
I'm guessing the fairly cheap "Consumer" oriented printers won't be capable of many of the parts you describe.
Also the Consumer printers yield a pretty crappy looking part that's best used in a hidden place. I'm sure all of this will improve in the future but for now I believe there's a limited application market.