A jazz festival doesn’t celebrate its twentieth anniversary without a vital aesthetic that perpetually dazzles its audience. Cheers to the VISION Festival, which reaches the big 2-0 this year by staying the course — its week-long program highlights the musicians who helped fuel the event during its first two decades, improvisers who forgo established rules whenever it seems wise and forge a personalized trajectory. From Amina Myers/Henry Grimes to Marilyn Crispell/Gerry Hemingway, an array of duos seems fetching this year. Saxophonists are a mainstay as well. The gnarled verities of Joe McPhee, the fierce arias of David Murray, the lyrical roar of Tony Malaby — each, repping a lineage that reaches from (participants) Marshall Allen to Ingrid Laubrock, holds forth at Washington Square’s Judson Church. With dance and poetry weaving between the instrumental shows, Vision’s multidiscipline interests are sated as well. And if you need two words to put your butt in a seat, here they are. Roscoe. Mitchell.