In my humble opinion, the foam style quivers do dull the blades a tiny bit, but I like knowing my broadheads are tucked away safe and secure when they're in the quiver.
I bought a nifty little broadhead sharpener at my local archery shop that has 2 small ceramic sticks set at the correct angle for broadheads. I believe that Bohning makes it. I carry it with me and just a couple of swipes and I know my blades are as sharp as when they were brand new.