As one of my esteemed colleagues suggested yesterday, this is a band that perhaps suffers some from being seen in the cold light of real life. Which is to say: appearances are not Yeasayer’s strong suit, unless you go in for the Burning Man thing. Tonight’s ensembles are no exception. But “Ambling Alp” is a jam, a jazzercise self-help seminar of epic proportions; by the end, even Dick Cavett seems impressed, and that man has seen a lot. A hundred dollars to anyone who can reconstruct what he whispers in Anand Wilder’s ear.