I think the one unit that sticks out to me that would have the greatest impact to improve the team is WR.
I would be a big proponent of signing either Amari Cooper or Keenan Allen as a vet to play alongside Nabers.
After Nabers, no one really sticks out in the group. I like Robinson but he is limited to slot only and has some limitations. Many of the top teams have a stud at WR and a borderline 2nd stud. Cooper or Allen would give us guys that can play slot or some boundary and basically between the four of Nabers-Slayton-Robinson and one of Cooper or Allen, a nice rotation at the position.
This is a win now year as mandated by Mara. Figure out which one has more left in the tank and sign them.