Great film, though I enjoy the first half much more than the second.
Carl should realize Muntz is there by the several clues he's given, his fandom. Carl's intelligent and able, so senility isn't an excuse.
Russell shouldn't be angry at Carl when Muntz steals the bird. Carl tried to save the bird, then Muntz lit his house on fire, so it overtook priorities. Then Russell takes this as betrayal? More so we're pencilling out the beats of a screenplay, and Carl has to formulaically lose everything, so we have to make the kid mad for no reason.
Did they not shower once they got back to town? It's not even cute to have them still disheveled for the ceremony, it's just weird.
So many great sight gags. The dogs pouring the champaign takes all.