I would like to suggest a frequent buyer's program.

Currently you have the following rewards program set up ...

Product Review Posted:  5 Points
Gallery Uploads: 3 Points                         
Approved FreeStuff Uploads: 20 Points         
Approved Tutorial Uploads: 30 Points              
Product Uploads: 25 Points                             
Approved Contest Submissions: 20 Points      
MarketPlace Purchases: 5 points per $1 spent for all members.
7 points per $1 spent for Prime Members.

I would like to suggest the following addition ... at the end of the month you run a report to see who were the top Prime buyers were.

Those who fall in the top 40% earn Bronze status and receive an extra point for each dollar spent. Those who are in the top 20% earn Silver status and receive an extra two points for each dollar spent IN ADDITION to the 1 point already received from the Bronze level. Those who are in the top 10% earn Gold status and receive an extra three points for each dollar spent IN ADDITION to the 1 point already received from the Bronze level and the two points from silver level. Those who are in the top 5% earn Platinum status and receive an extra four points for each dollar spent IN ADDITION to the 1 point already received from the Bronze level and the 2 points from silver level and the three points for Gold level.

To summarize :

top 40% = 1 extra point for each dollar spent

top 20% = 3 extra points for each dollar spent (1 point for bronze plus 2 points for silver)

top 10% = 6 extra points for each dollar spent (1 point for bronze plus, 2 points for silver, 3 points for gold)

top 5% = 10 extra points for each dollar spent (1 point for bronze plus, 2 points for silver, 3 points for gold, 4 points for Platinum)

This will create competition among your buyers. Suppose someone purchased $100 worth of stuff and they hit Bronze level and get an extra 100 points. They will be thinking "Maybe if I spent an extra $10 or $20 I might have made silver and got an extra 300 points instead of just 100 points"