For grey stamps @acebren is on point.
As for 2D vs 3D, no one cares about that except for me who wrote this article. 
I’m pretty sure 99% of the collectors don’t even know both variations exist. So it won’t affect the value (unless you have a 3D stamped Red Cheeks Pikachu, then it’s worth quite a bit more if you sell it to me 
).
Greetz,
Quuador