Ray is a great shooter, I love Ray, but he does not fit this team as currently constituted.
Ray is best when someone else creates a shot for him and all he has to do is finish. He has lost a step so his running of screens is not freeing him up in the same way it used to. His current style of play (shooter that needs someone else to create his shots) is a luxury that will push a good team over the top. It is not being fully utilized on this team.
My thought would be a trade centered around OJ Mayo for Ray Allen, they would have to include a guy like Arthur (out for the season free agent after) to make salaries work. On Memphis Ray would be much more valuable than Mayo is because they have shot creators. Both Mayo and Ray are free agents at the end of the year so it would be beneficial to both teams.