There are some who say that Dr. John—the high priest of psychedelic swamp blues—is getting old and starting to stumble. To those some I say: Don't go see Dr. John because he is the soul and flower of New Orleans music, because he used to play with Professor Longhair, because he recorded his first album on studio time stolen from Sonny and Cher, because he was the inspiration for Dr. Teeth, the bandleader on The Muppet Show. Go see Dr. John because he's been playing both old and new tunes on this tour, sampling widely from a career that has already ascended to the status of legend. (Jazz Alley, 2033 Sixth Ave, 441-9729. 7:30 pm, $26.50—$28.50.)