David's scientific prowess. In one of the mystery books, he reprograms a metal detector to only go off if it senses gold (he was looking for a class ring that had belonged to Joe's dad that Joe had lost prior to the story).
How the main trio can always deal with the bad guy of the contemporary story without stooping to their level.
In the "The Prince and the Pauper" episode, she gets ready to tear into Mr. King when the latter insults Joe's coaching skills. Sure, she got stopped by Wanda but it was still pretty cool.
In the "Robin Hood" episode, she shows up in the middle of Joe's protest and when he tries to explain himself, she tells him that he's standing up for what's right, what she and his father raised him to do, and that he might be in trouble with the school but he is not in trouble with her. Then when the vice-principal shows up and starts to bad mouth Joe, Ellen shuts him down with the statement that she's proud of her son and that she doesn't care what he says about it (okay; not in those words but that was the sentiment).