Here are some tests I did just using Vue functions for displacement, trying to capture some of the complexity and look of real (big) rocks. (So this is an attempt to create everything within Vue)

Before I post some pictures let me say that I do not claim this to be the best possible way, or that this is the way to go at all. Also this should not question any other workflow that has been suggested.

The renders all used the same basic function. This is not a function which is especially elaborated. But it was interesting enough to play  with, and to find out a bit how the look of Vue rocks, on which the function was applied to, could be changed.
No baking has been applied before rendering the "rocks" in order to preserve as much detail as possible. Btw. the contribution of the color to the details is only minimal.
The lighting model used was Global Radiosity ( Global Ambience did not look nice).

In some cases I had trouble getting rid of displacement artifacts. Playing with the various quality options, or replacing critical noise nodes, seemed to help.

Of course, when using fractal noise for bump displacement, without first converting into polygons, takes longer to render. However the benefit is infinite amount of detail (which certainly makes sense when rocks are placed in the foreground).

http://www.eonmusic.ch http://www.artmatica.ch