The Futures of America songsters are part way through their performance with "Has Anybody Seen My Gal" and a roster of ecstatically optimistic personalities is preparing to whip the giant crowd into a positive frenzy. Then Kansas City political whiz kid Joe Serviss leaps on stage to declare Thursday's huge all-day positive thinking rally the greatest in the entire world. Master of Ceremonies Ty Boyd, billed as a "sponge for knowledge," calls it "the great experience of our time."