My experience with rosters is that the less-crunchy characters, or characters that are specifically not beautiful, or powerful, or special - they don't leave the roster. Every now and then you'll get one of them taken by someone new - who then laments not taking that uber-looking guy that had been available, back when they had the chance.
If the goal is to give people a feel for the RP of a place without having to CG a character, I don't know how useful throwaway characters would be. Current active chars (not players, mind you, but their characters) wouldn't have some specific reason to draw them in. What impression do you want to give new people?
A suggestion I might have is to gild these wilting flowers. If someone takes Footsoldier #356 off the roster, have it notify people in the military that So-n-So's reenlistment date is upcoming, and they should all be making their best effort to keep him within the ranks. It's a reason to RP. If someone takes Petty Criminal #837 off the roster, have it notify other criminals that he recently got out of jail and that they should find out if he snitched on someone/throw him a welcome home party, etc. Basically little plot hooks that would make sense even if they happened every single day.
TLDR; there's nothing quite like a character with no plot hooks or ties to other characters or organizations to cause a new player to never log back in again. There are obviously going to be exceptions to this rule because people are individuals, but by and large, you want to draw new people in, not set them adrift on an open sea and hope they wash up on the shore of an uncharted island of exciting RP.