Even when Sparks is touring behind a weak album--such as its current "Music That You Can Dance To"--the band usually comes through with enormously entertaining concerts, fun and funny affairs that promote a sort of grinnin' dance fever. Most of those traits held true Saturday at the Pacific Amphitheatre, but parts of the show suggest that the Mael brothers have grown very tired. The band often sounded as if it were playing by rote, while other aspects of the show reflected similar indifference. They even played the title song from the new album twice. Is the spark gone?