I haven't found any references to using 3D printers to produce modelling aids. I've been working on a version of the Miniart WWI omnibus for a while now, and those who have attempted it will know that there are many fragile parts. In the course of handling the model I managed to break the rear grabrail which has a fairly complex shape.
I used my 3D printer to make a bending jig to produce the shape accurately, and after a few trials with copper wire:
I made the final part in brass and attached it to the model:
Since then I have made a jig to accurately reproduce a number of identical brackets:
A jig for filing an accurate groove in a 3D-printed dome light fitting:
And various drilling, shaping and assembly jigs:
I hope that this post provides some useful inspiration, I'm sure that forum members will come up with many imaginative and useful solutions!