Changing the judges panel wouldn't be the greatest idea. It'd take a chunk of the originality of the show. Altering the panel each season sounds more reasonable than having grown up with these 3 then suddenly replacing any of them.
I thought Quentin was cool but then the volume of his presence was just too, I don't know, over the top. I liked his honesty, but boy, his comments on Diana were unnecessarily harsh.
I thought Pete Waterman from the UK show created good honesty (on Kelly on World Idol), and the bickering between him and Simon was amusing.
I thought Gladys Knight from both season 2 guest judge and American Juniors had toned comments that seem comfortable for the show. Like she knew exactly what she wanted to say.
Bottom line, use them as guest judges. Don't replace the throne of Randy, Paula, and Simon. When I think about it, if I see in articles or episodes "your judes, Clive, Gladys, and Simon," it just doesn't work.