Here are my thoughts:

1. My issues with the prequels are many, and Jar Jar isn't really one of them. For a detailed look at how I would have written the prequels, read this if you're interested.

2. I have no issue with the Ewoks. The underline the entire point of the saga - ie the triumph of courage with limited resources over faceless technology with multiple resources. David and Goliath stuff. Jar Jar plays a similar role in the battle of Naboo.

3. More specifically, it is Jar Jar's clumsiness that causes much of the significant damage delivered to the enemy droids in said battle. The message? You may think you are worthless and clumsy, but you too have a part to play in the scheme of things. A message entirely in keeping with the inclusive Star Wars ethos.

4. I don't find Jar Jar that annoying at all, to be honest. Again, he's entirely in keeping with the general weirdness of the various aliens and space creatures of the Star Wars universe.

5. You make a very good case here, about the racial divisions between Gungans and humans on Naboo.

Despite all this, no, Jar Jar is not the greatest Star Wars character. :)