onQ, I'm sorry, but I feel like you don't fully understand how dreams is rendered. Definetly, a volumetric representation of geometry can allow for some rendering features not possible by pure poly-based models. But those are simply not leveraged by the specific implementation dreams is using right now which apparently is targeting 60fps. This might have changed, but as of their siggraph presentation, all volumes are rendered into a regular g-buffer, so all the exoticness of their rendering system stops there. The lighting is then done using data from that g-buffer not unlike that of most modern games. Whatever special sauce their lighting system has (if there's any) could be perfectly usable into rasterized triangle based assets. But mostly, I think most screens look good because MM has some damn good artists. That scene might be geometrically simple, but that minimalism deceptively hides a lot of good taste from the artists side on picking out good color choices, interesting shapes and proportions, and an expressive light set-up.
I think things will get interesting if they manage to implement a volume based lighting system. They had something like that for LBP2, and Evens mentioned the work of frostbite team on their Unified Volumetric Rendering, which is actually quite similar to LBP2's. They sure use a lot of scattering lights, and that's one of the key aspects of LBP's surreal look, it would do a lot of good for dreams, but might be hard to get working at 60fps... lets see.