I think it's a mistake to split the boys up. The show is at its best when the 4 interact. Even Cartman's show (w/Stan's sister) wasn't asfunny as I thaought it would be. And the last 2, one focusing on Stan,the other with Kyle and Kenny, were just about humorless in my opinion.
Kind of like when KISS put out 4 solo albums and all flopped!