Dreams are welcome! The idea of "legend" in our theme is vast and can indeed refer to dreams in some way.
Myths and/or Legends is a large idea that can link with a very lot of projects, from Mythology to History, going through Urban Legends and Modern Myths. You can even create your own myth, in a scifi world or a fantasy story, as you want :) Just make sure to turn it well to fit with the theme (also you'll have to wait for the secret theme to be revealed on day 1).
Anyway I'm sure your idea of dreams is excellent, so go ahead! Good luck and most important: try to have fun!