I thought it was quite nice of Lucas to not only not contradict Dark Empire, but imply it could be correct. Having Palpatine/Sidious have some deep, dark secret of immortality (that apparently can't save you if you're not awake to use it, like Plagueis) plays right into Dark Empire. Cheesy or not, Episode III did strongly hint that it could be true, just like how Lucas left a big hole open for the EU by not only not saying that Obi-Wan and Yoda were the only survivors, but having Obi-Wan rig the comn system to tell any Jedi who had survived to that point to flee.
Yes Dark Empire is pretty over-the-top, but so was the Clone Wars series which Lucas very explicitly had a hand in. It has always seemed that the most powerful Jedi and Sith had powers bordering on super-heroic. In Ep I, both Obi-Wan and Qui-Gon used superhuman speed that would look like a comic book, they take long falls, make incredible leaps, and act with inhuman precision. If Jedi wore spandex and capes instead of quasi-monastic robes they could pass themselves off as an League of Superheroes instead of a monastic order. Of course, high-level D&D PC's could do the same thing too.
Since Lucas was at least not openly contradicting the EU, paying attention to the idea that excessive use of the Dark Side could be physically corrupting could help explain his withered, decrepit look, especially when he was on the edge of defeat from Master Windu.
