Can't find it now, but someone must be familiar with the behind the scenes video where the LFL cgi artist is working on Yoda for Attack of the Clones. In the video, the artist says he is trying to convince Lucas that Yoda can be done convincingly in cgi. It's as if Lucas has higher standards for Yoda or something. I don't remember Lucas acting all that resistant in the video. But it is very possible Lucas was more resistant since Yoda seems to hold a special place in his heart - he does not authorize exploration of Yoda's backstory or species, for example. It's one thing to respect him for!