Setup a suggestion/voting section on your affiliate sites, like Dreamhost has for their customers. Customers get voting points, say 40 and can spend them on voting FOR or AGAINST a suggestion. They can submit suggestions too, that can be approved and assigned a credit amount.
Code:
2005-09-19 Mail - Webmail Replace squirrelmail with RoundCube (http://www.roundcube.net/). [ For it ] [ Against it ] 5 credits
2005-09-19 Home - Account Summary Allow moving of domains between accounts. [ For it ] [ Against it ] 3 credits
2005-09-19 Mail - Announce Lists Send unsubscribe email notifications to users when they unsubscribe. [ For it ] [ Against it ] 4 credits
2005-09-19 Goodies - MySQL Allow database names to be re-used. [ For it ] [ Against it ] 3 credits
An example above, shows a few different suggestions that had been made and the credit amounts, etc.
You could reward your best affiliates with more voting credits to spend, and they can make suggestions about what they would like to see in your program. The votes will add up and show you what your affiliates want most, or do NOT want most.
Should be very easy to implement, if you like this idea.