I strongly suspect the official explanation is "movement is cool". But we could compare Spock's hot rod with another high-performing spacecraft, the Orion vessel of "Journey to Babel". Its spinning structure in the TOS-R rendition might indicate a way to run an exceptionally powerful powerplant or drive by dissipating... Well, something
to the four subspace winds with the spinning motion.
I mean, it's not as if heat dissipation in vacuum would be boosted by spinning. But one could imagine it boosting the dissipation of heat or a comparable property into a transfer medium (say, a very hot blade of a kitchen electric mixer spinning in water, rather than just staying still - thus encountering "fresh" cool water rather than just already heated-up water with each revolution) - and Trek has its vacuum filled with the "subspace" medium...