Ironically of course if all you needed was a spot up 3pt shooter, and taking salaries into account, you might actually do as well with Reddick. Kevin's value is that he is more than a spot up shooter, and his cntract reflects that. If all he is going to be used as is a spot up shooter then there are a lot of guys around the league who can fill that same role far cheaper, freeing up money to be used on other positions.
Of course I think the inital premise is flawes -- we don't need soft defenseless shooters of any stripe, whether it be spot up shooters or major scorers. We're getting great shooting out of guys giving us a lot more than just their scoring -- that's ideal.