Donating at the $4,000 level is an invitation to be a part of the process and your feedback will be welcomed. You will be welcomed into meetings ( most likely via Skype or Google hangout ), able to view and play any work-in-progress elements, give feedback if you would like, and your name would be featured as 'presented by you' in the game splash screen and credits.
You will also receive all the previous rewards as stated on the campaign page. That said, you are not expected to contribute labor to the project or increase your work load, and your pledge through Kickstarter is a donation.
If you have further questions about this reward tier, feel free to message us!