Daydreams are useful to help us solve problems creatively, while our dreams at night are more negative than our everyday experience. I don't see any reason to assume that our night dreams are any more negative than our day dreams. So both dreams could fall under the same category as pragmatic problem solving tools. They don't sugarcoat the problem like us humans normally do, making them effective.
I see myself writing up a huge report on these ideas, replete with randomized groups and graphical representations, I see myself anxiously awaiting the day I receive the editor's verdict, and I see the paper returning, with two words in red ink on the back. Keep dreaming.