According to the Metropolitan Playhouse ''From Rags to Riches'' has not been revived in New York for more than 100 years. After seeing the play you'll wonder if the last troupe to stage it has yet recovered from the experience. A sprawling tale assembled from dozens of styles, genres and plots, the show is by turns slapdash, bewildering, rousing and ridiculous. It's also more appealing than it has any right to be. ''From Rags to Riches,'' first performed in 1903, was written by the ''Master of Melodrama,'' Charles A. Taylor, who in 1892 had five plays running at once in New York. Parts comedy, drama and thriller, ''Rags'' centers on an impoverished brother and sister who will soon inherit a fortune. They are thwarted by a Snidely Whiplash-type scoundrel, his scheming partner and an opium dealer, and simultaneously pursued by their long-lost parents, who hope to re-establish the family. [ABSTRACT FROM AUTHOR]