To me, having AAs for the Three Caballeros in the finale scene would be a bit jarring, after seeing them in animated form throughout the rest of the ride.
I know there's precedent for mixing 3D and 2D representations of the same figure throughout an attraction -- but even in a ride like Winnie the Pooh, where the effect is supposed to be suggestive of characters literally coming off the pages of a storybook, I find that tends to disrupt any suspension of disbelief. (The last scene, with a Piglet figure sitting in front of flats and painted representations of the other Hundred Acre Wood folk, has never worked for me.)
I think the disjunction would be even greater when the same characters are shown over and over, moving fluidly in "2D" animation, and then suddenly appear as AAs that, however sophisticated they are, can't squash or stretch or do any of the things that "they" have been doing throughout the ride.
I certainly wouldn't complain if someone decided to remove all the video screens and populate the entire Gran Fiesta Tour with high-end AAs of Donald, Jose, and Panchito. However, even if that were to happen, I don't know if the ride would be significantly more popular than it is now.