Fisher has said Spruce will need to make the transition to the slot to make it in the league. You can't call the guy the next Danny Amendola then say he can play on the outside. To me he is a JAG like Greg Salas overachiever solid hands, solid routes, but highly replaceable and will need to schemed open.
Spruce is clearly behind Marquez and Cooper. Can he be a marquez level special teamer? I don't know, but WRs who play on all special teams like Marquez are hard to find and if he cant do that where is his spot? Higbee, Cooper, Marquez and occasionally Kendricks and Tavon will all get reps in the slot before he does. Rams need guys on the outside and their only clear options at this point are Tavon, Britt, and maybe Mike Thomas. I would rather give that 6th WR spot to someone who could be more sucesful on the outside instead of adding yet another slot option.