I think a better way to capture changes in demand would be to base the reward on the rate of change of the difficulty instead of the absolute value of the difficulty. If the difficulty is rising rapidly, the block reward goes up. If the difficulty isn't changing, the block reward goes back to the standard 50 coins per block. For example, if the difficulty re-targets from 1,000 to 1,500 then the amount of coins per block goes to 75, if, at the next retarget the difficulty stays at 1,500 then the reward goes back to 50, if it jumps to 3,000 then the reward would go to 100. This keeps technological breakthroughs from having a permanent effect. The exact percentage to raise it, and how long to keep it raised would have to be determined.
Do you mean the opposite (a high percentage retarget would net less coins per block) because it seems to me that if I build a device that generates 5 terahashes/s (to be VERY extreme) the next set of blocks (which would happen quickly) would create far more coins.