City Engine is not so much a rendering enviroment like Vue and Bryce as it is a tool for laying out cities. It does have it's own "enviroment" and rendering engine, but these are more for visualization purposes, and not for photorealistic purposes.

I don't actually know whether or not Poser files can be imported into it - it never occured to me to consider that.  But, I kind of doubt it.

City Engine is not really designed to replace Vue. Rather, itin theis particular case, it is designed to layout streets and buildings that can be imported into Vue.