Okay, here's my reasoning behind why Yoda and the Emperor should never be seen with lightsabers. I'll focus on Yoda, but similar reasons apply to Palps:
Yoda is like the Buddha. He's someone who's been enlightened, who is perfectly in tune with the Force and nature, and uses his unique position to guide others toward this path. He's, for lack of a better way of putting it, better than using a lightsaber. Beyond it. He doesn't need one. He's the perfect Jedi, and showing him fighting just like any other Jedi - good at it though he may be - cheapens his status and makes him no different than any other Jedi. (This will bring me to another point later, but I'll tackle Palps first.)
Palpatine is similar, but on the other side. He doesn't fight, he's mastered the Dark Side so well that he doesn't need to - he manipulates others into doing his bidding. He has everyone around him wrapped tightly around his finger. All he cares about is controlling everything, and he's damned good at it. He's the perfect Dark Side master (I'm trying to avoid the term "Sith" here because I hate it), and, again, showing him fighting cheapens him and makes him no different than Vader or Maul or Dooku.
Now, back to the point I wanted to make from Yoda. The Force needs to be a religious thing again. The Jedi shouldn't be the Republic's fighting force like they're made out to be in the prequels - they work outside of the Republic. They're trying to become in tune with the Force, much like Buddhism's ultimate goal of reaching enlightenment. They should be highly-regarded, almost holy figures that try to keep the Force in balance, and only interfere with things outside of their own group when this balance is threatened. "The guardians of peace in the galaxy," and all. They practice lightsaber combat almost as a form of meditation, like martial arts. They only use it when they must, and they certainly DON'T flip around all over the place wasting precious energy the way they all seemed to do in the PT.
In other words, the Jedi use the Force to find spiritual enlightenment, and only fight when the Force is at an imbalance, to right it. The Sith use the Force for personal gain, which causes the Force to imbalance itself, kind of like a cosmic Karma. That's the only difference, that's what the "Light Side" and "Dark Side" are.
At least, that's how I feel it should be portrayed. It's in line with everything that's said about them in the OT, but completely shattered in the PT.
Unfortunately, I think the existing material in the PT prevents such a depiction, which is very, very sad.
