Just to clarify, in one of the scripts to TESB, Yoda does indeed have a lightsaber fight with the ghost of Kenobi.
And yes, I agree that giving Yoda a lightsaber was lame (just like most every other decision in the PT), but I wouldn't have minded seeing him use a saber just once, and similar to how he decapitated those soldiers in ROTS. Quick and deadly. And that's it. And only in the direst of circumstances.