When it comes to the currency, I would like to discuss about an another idea that some games or forums are using, but not in a wide range.
Instead of getting more and more money/credits/bricks each time you do something good or bad, you will have a maximum of 100 money, and can only achieve or loose from different ways.
10 from amount of uploads.
10 from amount of comments.
10 from reputation.
10 from classification of owned add-ons.
10 from good classifications of other add-ons.
etc...
If you e.g. loose reputation, you'll loose your points, and vice versa. The total sum of money will then give you special abilities, like giving access to the RTB API, or uploading add-ons.