I generally use subdivision (in the edit object panel) in order to make rocks smoother.
I have a collection of even smoother rocks edited in Hexagon, but the Vue ones generally look more realistic as they retain some sharp edges.
Using object parametric mapping generally helps get rid of most of the texture stretching.

Here is a test made with my bitmap based textures. I used displacement mapping on the two foreground rocks. This gets more natural, less uniform bumps. Moreover, the rock at the left is an imported one and displacement makes it less smooth.

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