Ok, so we may not want to recommend 3D Printing the engine mounts or components for your seat belt but 3D Printing cosmetic parts for your car is a perfect way to tidy up those little details that make your car feel complete. Especially when the manufacturer no longer offers the replacement parts for sale and/or they are incredibly expensive and hard to find...
Also, professional looking add-on parts could be made. I have a 2012 Chevy Orlando with automatic; 'D' is at the bottom of the pattern, and there is a 'manual' mode you get to by moving left from 'D'. But since the labels are on the left it looks like you maybe you need to pull it left to get into 'D' (http://www.gm.ca/images/vehicles/2012/chevrolet/orlando/chev_orla_int_ph_big_01.jpg) , and this works fine until you notice that the engine is really loud since it isn't upshifting. Yes this happened the first time someone else drove it.. And, I have accidentally bumped the lever to the left from 'D' myself more than once, this has no immediate effect (other than to change a gear indicator on the display) and so again, you don't realize it until you notice it isn't shifting. Solution: a plug that fits snugly into that area to lock out the manual mode, and which can be pulled out when needed.
If anyone from Chevy is reading this - it should be necessary to do something unusual - such as pushing the shifter button extra hard - in order to get into manual mode. Or, have the car tell me verbally that "manual transmission mode is selected".
I recently finished my Master Degree where my thesis was about utilising AM for the reverse engineering of obsolete motorcycle parts. It is being done on a commercial scale (albeit small) here in the UK using a variety of processes.
The thing that I found was the same problem over and over again, getting the geomtery in a format that can be manufactured. I am an experienced design engineer with over 20 years post graduate experience and I manufactured several parts including fascia panels and water pump impellors but even I had issues with measuring the components. It will get easier as new technologies emerge in geotry collection but it is still tricky at the moment.