A few quick thoughts. Clearly Plato's works are dramatic too. They are also, as you suggest, dramas of ideas -- of course structured very differently to Zarathustra. But my sense is that the "real" point here is that an Idea dramatizes intensive spatiotemporal dynamisms. It might be worth contrasting this part of D+R with The Method of Dramatization, a short address to a philosophical society conveying some of the essential elements of Deleuze's philosophy of difference, and in particular the structure of Ideas as spiritual expressions or automata.
A "classical" Deleuzian example here might be the idea of truth, which possibly remains obscure unless other concepts are made to resonate with it. That is: unless one applies the method of dramatization to discover beneath it other forces, to find or discover the means to relate it to an essence or future. So in the case of the truth we have the jealous man, the inquisitor, etc. These are not psychological profiles but more like dramatic conceptual personae. A question here for interpretation might be which sort of forces, which sort of lives and spirits and feelings Nietzsche is in conversation with in TSZ, and how they might be different than those in Plato.