Brad Smith does an awful lot for the Jets. He is a great guy on coverage units. He always seems to fill the lane and make a tackle when a returner appears to have a lane. He is the personal protector on punts. He is a dynamic threat in space. He is a Wildcat quarterback. He has taken 3 kickoffs back for touchdowns since December 2009. These are all excellent qualities.
The thing is they are nothing for which a team has to pay top dollar. They are not tasks teams sign players specifically to fill. Teams look up and down their roster and can usually find backups capable of filling these roles. Smith is a unique player, but a part timer does not have the value of a full time difference maker and should not be paid as such or prioritized. These roles are relatively easy to fill internally. Joe McKnight himself appears capable of handling a number of them.
This has to factor into the equation.