It definitely uses both cameras in Twin mode, it's just that the difference is rather minimal in most cases, but it's still there.
I don't think a camera setup like this is capable of as much as you are hoping. The monochrome sensor does take brighter and sharper images as there's less filters light has to go through, but it can't just magically improve a color image as it has no color information. My understanding is that it can bring out a bit of detail in the shadows and possibly be used to for some better post processing, but that's about it. I do think Nokia could make it have a larger impact, maybe with more manual settings, but it still won't blow anyone away.