Only the population bonus doubles and triples not the artefact production.

Yes, that's what it says in the artifact's description.

omg if the arti production trebled can you imagine what these would be worth?...you could virtually name your price

Um. Yeah. 3 artifact+300pop for 1 space. Imagine if their was no limit either. Aquatic planet with all 15... 45 produce, 4500 pop all for 15 space. Now. Think. If that was on a 2/3x mega rich... Very Massive... alert your legion. Get them to put all 15 of theirs on. 67 space (I can't remember the actual figure for very massive.) 904.5 Artifact, 20100 pop. + innate pop. I would love that planet.