Lucas was rather into the notion of history repeating itself, and explicitly saw the fall of the Old Republic in light of the fall of the Roman republic (with Palpatine as a very evil "Caesar")
and in light of the potential similar (future) decline and fall of the American republic. [Being pretty left-wing, certainly back in the day, he saw Nixon as an indicator of the Republic's moral decay. One might quibble with that, but Lucas's overall view of "how Republics die" is clear enough.]
This approach provides a rather obvious avenue for exploring a (reasonably) "good" Empire, in that you need Palpy to die (permanently) and some highly gifted ruler (akin to Augustus) taking power and reforming the Empire from a fascist regime into a more traditional monarchy. Another point of reference in history would be Qin Shi Huangdi in China, whose reign (like Palpatine's) was significantly longer than Caesar's, and (also like Palpatine's) much more draconian and brutal. And after his death, we still see that a highly capable man (Gaozu) ends up seizing power and founding the far more traditional (and far less monstrously oppressive) Han dynasty.
In the context of the original EU, the closest approximation of this that we get is the Fel Empire, but that hardly functions on the same scale (being essentially just a lesser successor state and a regional power). Indeed, SW
has no "Augustus" to match Palpatine's "Caesar". Thrawn is the most-suggested candidate, but he too is limited in his abilities. A masterful tactician, but if we go by his record, not on the level of "grand strategist" that a true ruler of that calibre requires. (As
@Bacle mentions: Thrawn's goal was "merely" to
influence Palpatine's successor. If we go with the Roman analogy that Lucas introduced, I think Thrawn would fit the role of Agrippa, not of Augustus.)
I have given some thought to this matter, and I think you could quite easily just
invent an Augustus-analogue for the setting. My own approach there was to take the once-mentioned side character Ederlathh Pallopides (who is Palpatine's grand-niece, and just four years old when he dies), and from there extrapolate that this girl must have had a family. I just assume that SW's Augustus-figure was some relative of her, and that in OTL, Palpatine had him killed early on (since Palpatine was no stranger to murdering potential rivals... nor relatives, for that matter).
It's all too easy, for there, to imagine a divergent history where Palpatine, like Caesar, is assassinated early into his reign, and this unnamed relative that he had killed in OTL ends up eventually succeedding him on the throne. (And founding a reasonably benevolent Empire that lasts for many centuries.)
I have some notes for "SW, but more like Roman history" (since I already wrote an essay on "Roman history, but more like SW"). In those, I call this hypothetical character "Antavioc Pallopides". (Which, yes, is just the laziest anagram for "Octavian" ever. Sue me.) Basically, he's the Emperor that Thrawn was hoping for, and with Palpy taken out early and the civil wars dragging on longer, he and Thrawn -- both young men at the time -- basically found the Empire together. Which makes it a rather different Empire, from a very early point on.
Palpy controlling both sides and having set up the whole thing as a trap from which there's no escape is generally considered Lucas's best idea in making the prequels. The narrative value of the idea is that the war cannot be won.