It's easy to assume that a documentary financed and self-released by Kevin Spacey will be a vanity project. Especially Monday's Tribeca Film Festival world premiere "NOW in the Wings on a World Stage," which follows the head of the Old Vic around the world as he stars in 200 performances of Sam Mendes' Bridge Project production of Shakespeare's "Richard III." But the documentary, which Spacey and rookie director Jeremy Whelehan (his former associate producer on "Beyond the Sea" and Old Vic assistant director) have been tinkering with for two years, is worth waiting for.