IMO, Marvin Williams is a great stretch 4 guy off the bench. He's not a starter at either 3 or 4, but the kind of depth player that a good bench needs. With that said, I don't want the Jazz to overpay to keep him. He's not a critical piece of the team moving forward. If they can get a quality pick or young player at the trade deadline for him. . . they should absolutely do it. Especially since there's a decent chance that a team will pick him up for a late run and his expiring contact. There's nothing to stop the Jazz from signing him back once he hits free agency if the price is right.
An ideal situation would be to land a something of value for him and Jefferson, finish the tank strong and then resign Marvin as depth for next year.