I guess that most of us are happiest when we translate work that we like, but often we need the money so have to do it anyway, and I agree with J that many texts have an important documentary status and need to be read in other languages: Mein Kampf might be an example of that. I have recently been translating some French poems by an important philosopher that are of interest because of the light that they shed on her life.
So here is a question: should we try to make good literature out of indifferent literature? Or is the question wrong-headed? (We would surely correct errors in a cookery book, for example.)