https://www.youtube.com/watch?v=TbSmrjmP85Q
Maybe that becomes a lot easier once virtual reality and 3d input devices become common, but until then I think there are better ways to use extra computation power
Making electronics can be pretty fun. http://powdertoy.co.uk/Browse/View.html?ID=915343
(It's not actually an ALU. All it does is add or subtract. But it was the best of its time!)
Of course the ~100 clock cycles latency for fetching from main memory has to be avoided, so you code in a language like c++ (like this project) and pack your data in big arrays in the order it's accessed in. Then processor caches and prefetching do the magic.
Particle interactions that usually imply quadratic runtime can be made fast by mapping particle positions to a grid and either looking up neighbouring particles in the grid or calculating large scale effects directly with the grid.
Personally, I think for this project the working whole and the value it provides as a fun educational tool is a bigger deal than architectural or development ideas that went into it (but I'm happy to be proven wrong)