I regularly buy sets for my kids.
I would buy some of the Ideas or Icons sets because they're neat but they are prohibitively expensive.
But since they would just be display pieces and I have no intention of disassembling them and making something else, I'm not above buying bootleg sets which are seriously dirt cheap. I recently ordered the Optimus Prime set for $35, the original is $180
I've been eyeing the Slug
But then I saw they made the entire arcade cabinet so now I'm eyeing the Metal Slug 3 arcade cabinet set:
Wuuuut.
If you're 3D printing, why not just print the finished design and be done with it? Getting the tolerances right on elements so that they fit together without sanding and/or gluing is a horrible pain in the ass.
What I've seen people do is get a parts list of a MOC they want to build, and then order individual (bootleg) pieces from Gobricks.