A card that is not made out to the user is fairly usless to anyone else. The card only contains your account number on the magnetic strip. Anyone could only find out your point balance by placing the card in a slot machine, but could not cash them in without the proper ID. Your personal data is located in the casino's computer.

I always erase the magnetic strips by waving a strong magnet over them.

Erasing the printed name and number is possible by using a solvent like GoofOff, but a slight impression is still embossed into the card by the printing process, which is almost invisible but readable. This process would lower the value of the card as a collectable.