As an aside, you "just lose" with vnodes and clusters of the size. I presume you plan to grow over appx 9 nodes per DC, in which case you probably do want vnodes enabled.
I typically only see discussion on vnodes vs. non-vnodes, but it seems to me that might be more important to discuss the number of vnodes per node. A small cluster having 256 vnodes/node is unwise given some of the sequential operations that are still done. Even if operations were done in parallel, having a 256x increase in parallelization seems an equally bad choice.
I've never seen any discussion on how many vnodes per node might be an appropriate answer based a planned cluster size -- does such a thing exist?