Only get the reward once, but you can repeat the mission multiple times. --- 82 RPG's defeated and counting- Currently working on - dotHack vol.2, Evolution 2, Fire Emblem, Final Fantasy Advance 5, FFXII
The only things that come back in repeated missions are the bosses, and the random enemies. The only things repeating missions are good for are 1. EXP 2. DMW leveling 3. Stealing from enemies to get those types of items.