The SFWA has recently simplified their membership requirements. It seems they are trying to open up their resources to more writers.
Their old requirements involved pay rate, advance amount, and date of publication. They also kept track of markets that were recognized as paying appropriate rates. Previous sales requirements were at $3000 for a novel, or three or more short fiction pieces at 8¢ a word.
Now the new sales requirements are much simpler. One must earn $1000 or over on their work to be qualified for Full Membership. Or they must earn $100 or more to qualify for Associate Membership.