I don't think it matters how cluttered a scene is, it's all about the composition. If the composition is good, the image will be good, and the viewer will get the point. The viewers eyes should naturally follow along a path to the point of interest. If your eye is not led to that point , it could seem pointless or just plain busy. There was at one time, a really interesting article on composition over at RDNA, that was 4 or 5 years ago though, I took a quick look right now, but couldn't find it. If you are interested in composition, Rosity has a art theory forum. It might be well worth looking into.
Shadows make a image extremely interesting, go beyond that and you've lost the viewers interest. When I first got into 3D stuff, I purchased a book called "Lighting & Rendering, by Jeremy Birn. There was a lot of interesting info, each chapter had a exercise for you to enforce that chapters subject.
My advice ....... lighten up
I think that if you improve the composition and introduce shadows, you'd come up with some kick ass renders

My own business always bores me to death; I prefer other people's.