Can one have nostalgia for nostalgia? Watching Grease--a '70s musical about the '50s--in the '90s is like reexperiencing déjà vu all over again. (Apologies to Yogi Berra.) I can't say I liked it back then, and I can't say I like it now, but the movie's camp value has soared: Everybody seems to be taking their lack of seriousness so seriously. As the hottest thing on two hips since Elvis the Pelvis, John Travolta is pure delight, but instead of building a movie around him, producers Allan Carr and Robert Stigwood threw together the cinematic equivalent of a high-school prom. Forget Grease. Where's Saturday Night Fever?