Since the typical raffle has ~120 entries, your chances to win are 1/12+1/11+1/10. That's about 25%. That means your 500 Credits will most likely earn you about 6 wins if this keeps up.... how about no? The whole thing must be a bitch to manually move the rewards all the time.
Really, the raffle should be monthly or something. Quadruple the winnings just so that less work needs to be done.
... ... or just keep the rewards as is, since 30 bucks per week sounds rather rough. 30 bucks per month is still rather generous.