Paula is next to useless in a judging capacity, but she is cute with Simon. I think Randy would probably be the easiest judge to replace. Losing Simon would most likely be a disaster to the spirit of the show.
I agree they need to change the age limit and the voting method. Hopefully they learned their lesson this year about putting through craptacular singers with "personality." It's really messed up the voting, which has been all over the place. If JPL or JS had won, the show WOULD have jumped the shark big time. The way they grouped people stunk, too. All the good people were in one or two groups so we lost people that were better than the "winners" from the other groups.
The themes need to be broadened. Gloria Estefan night was a bad, bad scene, and the other themes haven't been much better. The only "artist" night that worked all right was Elton John, beause he's done so many different styles.