It's never a good to tank for draft position. I hate that thought with a passion. Also, we don't have anyone new to develop that hasn't already played.
Honestly, at this point, I would trade Marshall before the deadline to gain players/picks for the future. I have a sneaking suspicion that he is going to be a major pain in the ass as a free agent. This team lacks talent on every level of the defense, still have issues with OL and have no speed on offense. I would hate to lose him, but we may gain through that loss.