Rewards seem to be the same as lvl30...just mire expensive
You have less regular card drops with LVL 40. Thus, you are more likely to get the SR and UR cards. Before you select DUEL on the LD, you can see a button that shows the rewards of the different levels...
level 30 drop common shared cards such as dragon treasure, secret of gallants, etc. level 40 don't.
Lvl 40 drop more higher rate of SR/UR compared to lvl 30. Also, no wooden box.