One issue that has come up, whether inadvertantly or not, in several posts is whether it is a better move to add a great/potentially great player at a position that is not necessarily an immediate need or if it is better to add a lesser/potentially lesser player at a position of need. In the interest of funneling the discussion into one thread where everyone can feel a bit more comfortable voicing their opinion, let's have at it.
Personally, I feel you build your team with great players. I have never heard a coach upset about having too many great players at one position. Good coaches can always find a way to make it work (within reason, i.e. having three great QBs is unhelpful at face value, but you can create value even then by trading).
I also understand chemistry arguements, and those have merit, but at the end of the day, character does not win games. You have to hope you have enough character in a room that if one guy loses his job, there are others to step up. Furthermore, if a player has so much character as to positively influence the team, I think it goes without saying that losing his spot to a younger, better player would not knock him out of a locker room leadership role. He would have the character to continue leading; you don't have to start to be a vocal leader.