Nice job finding the equation to calculate the centroid of the Chestahedron. The vast majority of polytopes require an algorithm to find the centroid, but for special cases of symmetry, this aspect can be used to intuite a formula.
Oh, and thx for clarifying the distinction of the volume centroid versus the vertex centroid. Now, I have to go off and find out exactly what that means (beyond the formal defintion, that is)...
The place to talk about Stella4D, Great Stella, and Small Stella. Feel free to ask questions about them here.