I own both programs. I have had bryce 5 longer than vue 4, and what i would say is to purchase Vue 4 over bryce 5.
Vue is a TON better, much more flexible, better materials, much better layout. As far as beautiful realistic 3d scenery goes Vue is much better at doing the job, vue also renders better, It even has a very nice lense effect setup. Plus if you like to animate anything, it is harder than crap to animate in bryce, to get smooth motion and everything. Vue does smooth motion automatically, with a much better key frame design to work with. Even has preset animated water, skys, clouds. Vue 4 is just a ton better and it's positeves out weigh bryce by far. what more can i say. Vue also keeps texture coordinance on the models perfectly when you import from you 3d max or Maya.
Don't make my mistake and buy bryce. I never use it anymore now that i have vue.