OK, so I'm back at work & I've asked the questions.
Our Design Engineers think that the easiest way to achieve the right texture would be to print the required part, then sand/beadblast the texture onto it.
This is partly because the accuracy of (affordable) 3D printers is not high enough to apply a fine grained surface texture, & partly because of the way in which printed objects have to be layed down - Most likely the exterior surface would be the first layer, facing downward, away from the print head.
However, if the surface that the plastic was being printed onto had the desired texture, then the printed item would 'inherit' that texture.
Thus, if a section of Amiga casing (treated with a suitable release agent) were used as the print surface, the printed part would have a matching texture.
My apologies for boring everyone rigid. 
Don't stop now! I like my plastic to feel, um plasticky. So, how hard would it be to make a 2 halves, clam shell sort of case that had simple plastic stand offs in the right places to mount a motherboard / circuit board to it? Then some self-taping screws hold the lid part on? Very simple, pizza box looking thing? Is that possible with todays 3D printers?
All I see is people making stupid little figurines and junk. See here:
http://i.materialise.com/I would call up and be like, um I wanna make a box, can I make a box?
And they'd be like, you can make your dreams, imagination come into reality.
And I'd be like, hoollly shit ! My dream currently is to make a box out of plastic! Am I crazy!?
And they'd be like, What about an elf ? Nope, I need a box.
I need to find the right 3D printer crowd I think.
