One thing the disaster at Wolf Trap has done is increase the color and variety of arts life in and around the nation's capital. Items: Maxine Andrews (one of the Andrews sisters) will be a guest star in the gala sponsored by the Gay Men's Chorus, May 13 at the Warner. Other featured attractions (besides the chorus and its subgroups the Sine Nomine Singers and A Few Good Men) will include ballerina Amanda McKerrow, soprano Marymal Holmes (second-place finalist in the Metropolitan Auditions) and others too numerous to mention . . . C.G. Sloan, art auctioneers, are asking for tax-deductible gifts to be auctioned off for Wolf Trap on July 31. If you can't give money, why not the family jewels, or that old Corot that has been catching dust in the attic? . . . Tour Designs, Inc., a travel agency that books tours to music festivals abroad, has pledged a $100 contribution to Wolf Trap for each booking received by May 31 . . . Project Renaissance, an educational enterprise in Gaithersburg, is offering a one-evening course to stimulate creativity for would-be composers who contribute $5 or more to Wolf Trap--tonight at 7 in the Stedwick Elementary School . . . and John Ferrante, the "bargain countertenor" who specializes in the music of P.D.Q. Bach, will give Wolf Trap 50 percent of the $10 patrons' tickets for his recital May 14 at the Flint Hill Preparatory School in Oakton, Va.