Equivocate; You keep using that word. I do not think it means what you think it means.
The only thing that can guarantees meaningful companion interactions is writing and word-count. Of course everyone has their own opinion on what is and isn't a good companion, but using Baldur's Gate II as an example, I think most of the people you can take on have a distinct voice, usually a quest that allows them to express some character and world-view. And that carries on to the newer games too, Dragon Age and Mass Effect are mostly remembered for the companions than the central storylines, that's how it is for me anyway, and their rosters aren't small.