FYI: I was curious how many non-financial transactions there are and used your prefix list to identify gamble transactions. Then I compared the total number of transactions for SatoshiDice with the sum of the total number of transactions of the 15 addresses listed on satoshidice.com based on the data provided by blockchain.info.
Turns out the prefix based filter identified 11'677'989 transactions at height 327'115 while the actual number based on full hashes was 11'124'066 at height 327'120 +-2.
Under the assumption those 15 addresses are the only relevant ones, then that's about half a million false positives.
And how do you get 11 million transactions in a block, when blocks can only have at most 4.5 million at most*?
* Unless they have non-standard transactions, which can't possibly be dice spam.