Regarding "enhancement" suggestions to Yoda:
Yoda blinking isn't a new thing... he actually blinks in the original versions of ESB and ROTJ.
Adding extra blinking to Yoda might also backfire... I think his not blinking excessively adds to his character's charisma (and I don't blink!) and zaniness.
Besides, a little woodland creature staring up at you and blinking while mugging for the camera is such a cliche.
Frankly, Yoda is probably the Muppet that needs the least amount of enhancements.
If you were going to attempt to "fix" anything about him it would be his motion when he's "walking" with his cane upon his first meeting with Luke. That looks really muppet-ish and fake. And maybe for a second while he's doing the "mine mine" thing it breaks the illusion slightly.
ROTJ Specifically:
I haven't looked at it frame by frame, but I'm told the shot of Luke flipping in the Death Star is an obvious stunt double with different colored hair than Mark Hamill.
When Vader has his hand cut off, at a certain point (I forget where) I remember thinking it looks really obvious that he's got a longer arm to create the illusion of a "stump." Perhaps that could be fixed somehow.
If you're going to kill off some major character in ROTJ, please let it be Jar Jar Binks. ;)