I would say neither are worth it. Palmer is #3 in the depth chart so unless they both get hurt. Which is doubtful, but it could happen. Remember the Eagles last year? And Leftwich only has a slightly higher chance than Palmer because he's backup. He might see some action because Brunell has had his problems as of late though.
16-team PPR Keeper League
QB: T. Romo, V. Young
RB: M. Turner, B. Wells, T. Hightower
WR: A. Johnson, J. Ford, N. Burleson, A. Roberts, J. Simpson
TE: D. Clark, J. Cook
K: R. Gould