Yes I would say its really important. If a person has the potential to earn money from a card submission they also have the incentive to start gaming the system (groups of people even) by rating their card highly even though it may not be the best card.

Also you really need to limit the voting by ip address, what prevents me from adding an affiliate link and then creating accounts with my 50 different email addresses and boosting that card to the top all for my personal gain...