We have developed our own penny auction module with a store credit module, (to Magento Certifed Developer Plus level)
We have tested it on CE 1.6, but it *should* work on all versions and more testing is required.
We are looking for people to try it out and give us feedback.
I realise your post is 1 year old. Are you still interested?
Personally I think this could be a great extension to be used in conjunction with a loyalty program, where users get auction credits in return for customer behaviour.