From my perspective, the amount of Karma something costs does not nessasarily correlate to the amount of RP that role is worth. Sure, some extremely roleplay based roles such as Magistrate or Nanotrasen Rep are locked behind a high karma thresh-hold, but I think the people who want to roleplay will be spending their karma on those roles, rather than less roleplay orientated jobs like Mechanic or Bluesheild. I think it's much the same for races. Someone interested in roleplay may pick up a Vox, and those who are not will pick up something else. Different jobs and races serve different purposes. Some people don't want to talk in Vox all shift, but want to be unique from Humans.
Heck, the second most roleplay orientated race in my opinion, IPC, is one of the cheapest species unlock.
People will unlock things in order of their preference, and I think raising the Karma price for Vox would just be a waste. It's a nice thought though, and I find myself agreeing with Kyet in the sense that the Karma system can have some issues, but this doesn't seem to be the thread to address them specifically.