I'd keep Lowrie and let him play SS. He may not be Alex Gonzalez or Orlando Cabrera....but he may be Derek Jeter.
Jed Lowrie needs to make an impact offensively to be considered on this Red Sox team. A switch hitting middle-infielder with good contact and power skills is tough to find. IF he becomes a hitter in the mold of a Nomar, Jeter, Tejada, Renteria...whatever....he will stick around and play SS no matter what his range or arm strength is like.
Lets remember that Lowrie is still very young and the more experience he gets at SS the better he will get. Perhaps his arm and range sit idle but his instincts will improve.