Of course it went up. Basically no one returned kickoffs last year which is why they changed the rules- so that there was actually potential for a play to happen again. Not a lot of guys are getting concussed on a play that doesn't happen. Maybe Kevin Kolb?
I'm not sure if you can have it both ways. A kickoff is by its nature a play that encompasses the whole field, and guys are going to run fast, run hard and inevitably collide no matter how you slice it.
Just make the *****-helmet mandatory for all special teamers and hope for the best.