I would think it would be a cool idea if you got one credit forever, but when you kill a traitor, if he has a weapon you can pick up, than you can sell it in the shop for a credit? that way you wont just steal the credits from Ts, you would have to get hold of the weapon, so detectives and Ts could still buy their (way more useful) items.
EDIT: also, i think it would be cool if there were a couple weapons that you could get that wouldn't normally spawn around the map, (nothing OP, maybe just binoculars or something just as crappy, but still useful) but, now that i think of it, it would be annoying if everyone got the same weapon every round, so i think it would be a great idea if you got a system similar to the T selection system, and made it so that depending on the number of people, a number of inno's would get 1 credit each (also you shouldn't be able to send credits to people) so it would be like, if less than 7 people, 1 guy gets credit, if there is a detective, 2 innos get a cred, and so on forth. (i would like this because than you could have the little joy of a special round without having to be a traitor)