I'm running 64-bit, and have for the last 3 years. I use the system for gaming.
Would you be more likely to buy a game that is 64-bit aware?
No, I wouldn't. Being 64-bit aware or not is not a consideration. What the game can do with that is a consideration. A 64-bit aware program is only impressive if it pushes the envelope. If there is no discernable difference, I don't care one way or the other if it is 64-bit aware.
In other words, for me to go out and buy something because of its capabilities, those capabilities must be clearly outlined. And just saying 64-bit aware is in itself not a feature. Double the map size is. Double the amount of AI factions is. 50% longer view radius in an MMO is. And so on. Prove that you can use the extra memory for something, and THEN you have a selling point.