"Meditation is not necessary for me."
Translation:Medytacja nie jest mi potrzebna.
Sounds a bit different to me, more like "I do not think that meditation is a necessary thing".
There are other examples in which an adjective is used with dla, e.g. in this unit "Te kolory i symbole są dla nas ważne". What is different about potrzebny?
I don't like it, it looks to me as if 'medytacja dla mnie' was one noun phrase. And the 'dla mnie' construction generally seems worse to me in such a sentence.
Everything else was the same as the answer except I swapped mi with mnie. What's wrong with that?
You need dative here, but mnie is accusative/genitive/locative. It could theoretically also be an emphatic form of mi, but isn't recognized as such, unless the sentence starts with it.