Michael Johnson is best suited for the position he fills with the Bengals, a 4-3 DE. In the 3-4, he would likely be too small for a DE. I'm uncertain how he would do as an OLB.
I agree that Brandon Spikes or Vincent Rey would fill a big need: to become stouter up the middle.
I haven't given up on Richardson. He needs to see a good sports psychologist in the off season to regain confidence. His hesitation in he backfield caused him to miss numerous opportunities,
We should let Franklin go in FA and pick up a NT in FA to strengthen the middle as well.