>But you can't construct a coherent version of the tripartite soul within a rationalist framework, yet Plato obviously did hold and posit a theory of a tripartite soul, so clearly he posited positive and dogmatic ideas here at least.
That's neither obvious nor clear; one could as easily claim that Plato obviously and clearly believes in a simple unitary soul, and whereas there's only two dialogues with a tripartite scheme, there's plenty that treat the soul as a simple one (Phaedo, Symposium, Meno). But again, I quoted the Republic *which itself says the account therein is flawed*. Let me add to that Phaedrus' equivalent:
246a
>So then, concerning its immortality, that's sufficient; but concerning its idea, one must speak in the following manner. What sort of thing it is, is altogether in every way a matter for a divine and long narration, but what it is like, for a human and lesser one; let us then speak in this manner.
So according to *both* Republic and Phaedrus, the tripartite accounts are less precise images, not doctrine. What's more, in the Phaedrus' case, you'd have to ignore what the whole second of the dialogue suggests: that the palinode is a piece of rhetoric meant to make Phaedrus into something more than a hedonistic lover of speeches.
>There's no skeptic theory...
I agree that there's must be more than repetitions on the Apology, but between the Apology itself and the apoeretic dialogues, we also have several dialogues consistently claiming that Socrates *does* know one thing: Erotics. (Symposium 177d, Phaedrus 257a, Lysis 204b-c, and Theages 128b) But by Symposium, that means he knows...his lack of wisdom. This can't be just set to the side, it's a consistent theme. If you said, "sure, but it can't *just* be Plato writing 35 dialogues on exactly that one subject," to which I would agree, but as per the treatment of writing in the 7th letter and Phaedrus, his dialogues aren't meant to say overtly what he thinks, but might nonetheless indicate something or other. That's fine, that work of constantly banging one's head against the dialogues *makes the reader like Socrates who still asked the same questions at the end of his life as if there were no progress or ultimate culmination he reached.*
As for followers, we know practically dick all about the Academy in Plato's day, and the most certain thing we can say is that it began as an informal meeting place for the remaining Socratics. We don't know how the dialogues were used or what Plato taught.
>I return to the notion that...
You keep saying this, but I'm not sure you know what you mean; you yourself are operating by modern canons of coherence instead of seeing what's in front of you: 35 dialogues that, as dialogues, can conceal as much as Heraclitus' sayings, dialogues in which Plato is never a character speaking for himself, the longest of which doesn't even feature Socrates, all treating the forms and soul differently.