3D printing technology is indeed amazing, and have improved in leaps and bounds over the past couple years. I still find it humorous that the attitude is that it can simply replicate anything.
There are a couple major issues with the idea of simply replicating NLA parts.
The first and most significant problem is how do you get a 3D solid computer model of the part you need to replicate? Yes there are optical scanning CMM's (coordinate measuring machine) that look at the part and output a file, but these are EXPENSIVE. One could measure using simple inspection tools also and then learn a 3D CAD program also, again not trivial both from learning curve and cost.
The second issue is that the range of choices for the material the part can be made from is fairly limited at this time. Also properties of the printed material aren't all that great, being that the part is made layer by layer the plastic doesn't have fully homogeneous internal structure. In other words its not all that strong, although both these issues are something that is improving with time.
I manage a small short run and prototype CNC machine shop. We have a few customers that use 3D printing technology for prototyping. Only one customer uses 3D printing for parts that actually go to an end user. These are hearing aid cases which don't require any great strength or durability. In this case 3D printing is perfect and it takes the moldmaking and casting out of the picture, greatly streamlining production.
For any parts that require durability machining from solid stock is still the way to go. This allows the part to be made from practically any material, not just a few printable polymers. Besides if you get to the point where you have a 3D model of the part, a machine shop could easily replicate the part too.
One neat resource for machined parts is eMachineshop (even if they are a direct competitor to our shop). This is an online interface to a prototype machineshop. You download their CAD software, draw your part then upload and they make it. Pretty spiffy!
http://www.emachineshop.com/