Like Yoshi the great said. People with programs such as photoshop has a huge advantage with people that has paint.
Sounds good but the problem is that there are over 6000 registered members. You can try to find only active ones but will be a lot of work.
This would be a good contest. After all it is a Mario Kart Wii forum. Just make sure it is not time trials. The biggest problem will be constantly adding and delete friend codes for the contest and different time zones.