They are cute and it's fun to watch them interact with the other characters in the Star Wars universe. I love Wicket and think the other Ewoks serve a purpose as residents of Endor. Even if they weren't referred to by name, they've become part of the Star Wars films and people love them.
George Lucas formulated the idea that an indigenous ethnic group should preferably overthrow the emperor during what was specifically created, at that time, to be the concluding chapter of Star Wars. They function to fulfill their objective of turning out to be the domestic group of Endor that overthrows the emperor.
The Ewoks may be one of the more irksome creatures in the Star Wars universe but they do actually serve a purpose. On the planet Endor, Luke, Leia, Han, Chewbacca, C-3PO, R2-D2, and the other members of the Rebellion try to destroy the Empire compound that controls the Death Star. Without the help of the Ewoks they would not have been able to get through the jungle and find the short cuts that the Ewoks provided. In other words they helped speed up the process.
Not only are the Ewoks fun, entertaining creatures, they also are a very important plot point. The empire would not have fallen without the help of the Empire. Additionally, the Ewoks make a powerful statement about the importance and value of the little guy and his or her ability to help.
They make the empire look weak and pathetic. Return of the Jedi would have been much more exciting had the Wookies defeated the Empire instead. Wookies are a lot more interesting and it could be an opportunity to reveal some of Chewbacca's backstory. They are strong and fearless yet they still appeal to younger audiences. I can imagine the fight being led by Chewbacca. Wookies have more reason to fight the Empire considering a lot of them have been slaughtered by the Empire in the past. Ewoks just seem like a merchandising opportunity. Wookies are more relevant so they should replace the Ewoks in this film.
The thing with Return of the Jedi was that there were many unnecessary things. Let's go through a few of them:
- Princess Leia Slave Scene: That was absolutely not needed. All George Lucas was (obviously) trying to do was please the teen male audience.
-Ewoks: That too was not needed. It could have been any species to help defeat the Empire. However (yet again) George Lucas was trying to please the audience that like cute little teddy bears.
Overall Lucas was trying to bring in new audiences to get people who aren't as enthusiastic about Sci-Fi films.