I've also experienced this crusty numbness that you describe. I think everybody that does this for a little while feels that way. I think it's a survival mechanism brought on by years of vicarious trauma.
For me, the meaning is found in the constant struggle back towards humanity. It doesn't matter whether or not you feel something. What matters is that you care whether or not you feel something. IMHO, to be human is to constantly struggle towards being a better person. As a species I think humans are fallible, fearful, lazy, and self-serving. The nobility of humanity comes from struggling to overcome these base traits to be something better- to transcend.
The work we we do is intrinsically humane. It's ironic that we have to lose part of our humanity to do it. Just remember, if you're a spiritual person you can connect yourself to the source of infinite love. Our time, resources, and feelings may be finite, but we can love infinitely. Strive towards that...
Good luck. And know that we have been there and we are all here for you.