Another thing that I think contribute to more sympathy for the Ewoks than the Gungans is that the Ewoks were real. You could imagine running into one while taking a stroll through the woods. They were real costumes with real people inside, this made them feel very tangible, like just about everything else in the OT. The Gugans were not real, I could imagine running into them in real life about as well as I could imagine running into Roger Rabbit or Daffy Duck in real life. They fact that they all looked pretty much the same didn't help much either.