I just don't think he has that much left in the tank. At best, he's a mild Branch upgrade, and even that's unlikely given the chemistry Branch and Brady share. I'll admit Palmer may have limited his production lately, but in your wildest dreams, what would you hope for from Johnson? 1000 yds, 8 tds in 16 games? Branch had 700 yds and 5 tds to go with a very nice YPC in 11 games with us, so it seems like a lateral move to me.
I wish Johnson the best, but I don't think he has anything to offer the team. If we go for anything at the position, which I'm not sure is even called for, I'd target a skill set that is less redundant. Maybe a big, physical body that can be an added threat in the redzone as well as deep. Even that, to me, is a luxury.