You're the linguist and me the translator, but I wouldn't do that. The number of native speakers who would say "more rich" is vanishingly small.
I agree, and I hesitated quite a bit, but in this case I don't really see any harm in accepting it. It'd be in case we're afraid of teaching non-natives bad English. I'll give it some though at least - thanks for the feedback.
Up to you, but I've seen a number of remarks/questions from non-Anglo learners of Swedish who don't have it clear that regular one-syllable adjectives almost invariably take the -er/-est form. That would be the harm: teaching poor English for the sake of teaching good Swedish. I know there are a lot of variables in what you do. Cheers, and thanks once again.