Like others, I would also like to keep Green, but [obviously] not at the max. While the SF position is a little shallow, it's not like Green is soooo much better than the next tier after him (like those that are above him are - Lebron, Durant, George).
The thing that is great about him is his fit on almost any team - on bad teams, he can take on bigger load of the scoring, while on great teams, he can slot in as a 3/4th guy or even a super-sixth man. His efficiency really doesn't change much either way. He really is a guy that most teams would like to have, which is why there is reportedly considerable interest in him.