Not unless they've a need.
There are certainly countries it's easier to get into with a passport for one of my citizenships than the other, and vice versa. Not having a pressing need to visit any of them, why would I waste money on a passport I'm not going to use?
If I was planning to visit a country that is more welcoming of the citizenship I don't have a passport for, I would certainly consider getting it (though probably not; the few places that would prefer it aren't particularly unwelcoming of my other citizenship either, but for other citizenships it can make a massive difference).
If I was expecting to have some need to prove that other citizenship for some reason, I'd probably get a passport.
If I was expecting to have to leave the country in a questionhurry (not a bad thing to assume as a possibility wherever one was) and the citizenships had very different treatments in many countries (in my case they do not), I'd consider having both.
I'm not going to spend time and money on a piece of paper that'll just get itself lost somewhere in my office though.