Good post. Interesting about how big a 3D printer like that could be. But with the U.S. improving it's rockets to carry massive payloads weighing 70-140 metric tons, it should be possible for them to get space worthy versions into orbit.
http://www.space.com/22572-giant-rocket-launches-secret-spy-satellite.html
You're right about robots not being able to repair on their own. I don't think autonomous repairing droids will be happening anytime soon, but if those robots were drone styled, they could potentially be controlled by a human to perform the repairs necessary and correctly.