Where payment is concerned, there is a way to have a 'fair' reward system for payment. There is a druid's cloak in the game. We have no idea what it takes to make, but it is in the game. Say it takes two silk cloths to make. Once you have collected two silk cloths, you use your account and make a donation and select the Druid's cloak award. This would allow you to make and equip a Druid's Cloak, if you have cloth making. It would not be overpowered, it would just allow you access to it.
In addition, there could be a black bronze sword called Gram. To obtain this you need three bars of bronze, ash, and a bear's tooth. Donate, select 'Gram'. You can now make and equip Gram. You need metal working to make it. It would do the same damage or slightly higher damage (like 350).
There is another payment system that allows those who make donations a special forum where they get inside information and are able to vote on future additions. Like what should be in first: wolves or horses (example).