You can choose a Value, Moderate and Deluxe - throw in a value - not only will some guests want/need one but if you need to pay for rooms left in the block, you will pay the value price (someone correct me if I am wrong).
If anyone is DVC - you can add less rooms to the block and the DVC stays count (just have to give them their reservation #) and you will meet the number of blocked rooms much faster.