I don't think that printers becoming household items would change the basic situation for copyrights. It will just increase the number of occurrences and make it less controllable. But it's not different than making a drawing of a known superhero. Unless you do it to sell the items of course.
One thing to consider though is the 3D file. Not everybody can 3D model, so for home printing to become popular there should be libraries online with 3D models (like you see for 3D graphical programs right now). The copyright owner can go after the site that published it and the person who put the file there (similar to what you see in this thread). One difference with the music industry is that these sites will likely be mostly original items (of which the copyright is owned by the uploader). So it will be harder for them to go after a whole site like music and IP companies are doing right now.
As to the Datsun boot badge, I expect it will be Nissan who owns the copyright. Possibly the trademark too if it was maintained. So, strictly speaking you would have to ask them for permission.
By the way, your question makes me think of this case:
http://www.jenkins.eu/mym-spring-2010/german-courts-toy-with -law-in-opel-model-decision.asp
http://jiplp.blogspot.com/2010/03/bundesgerichtshof-decides- in-opelautec.html
Interesting is to see the difference in tone between the two reports. The first one is surprised by the outcome while the second is not.
This also shows one of the difficulties of copyrights and trademarks. Outcomes can depend on local culture and specific parties involved.
If it comes to model kits, Lockheed and Boeing lawyers have also gone after model kit producers to get royalties on models of their planes. I've forgotten what the final conclusion was.
As to aftermarket product like for the i-pod, I've been wondering about that as well. I'm not sure where those stand if it comes to copyright. GW forbids it, but I'm not sure of the actual rules about this. Anyone?
@stop4stuff: thanks for the links. I missed that post. Hehe, one thing I like about what's in there:
Accessibility for someone with a visual impairment
It is considered fair dealing to make an accessible copy of a work for someone with an visual impairment if a suitable accessible version is not already available.
Nice