I tried to resist feeding the Troll.  I can't.

1)  You cannot destroy Bitcoins, you can only lose them (and they CAN be found, albeit with difficulty)
2)  With 700Mhash/sec, you're no where close to causing any real harm, you're losing what?  52 coins a year?  Who cares, there are 21,000,000.
3)  Every coin you lose, increases the value of the coins left in the network.  I applaud your efforts.
4)  You are INCREASING the liklihood that coins will be found by deleting your wallet.dat; because you're increasing the number of addresses that have lost coins on them.  You'd be better off having all of your miners send them to a single address who's wallet.dat you've already erased, just saying.

Welcome to Bitcoin.