I have an idea, not sure that this is doable.. but could be helpful in controlling the amount of storage we use. I know that I'm a big offender, and honestly want to do what I can to help here.. but it isn't very often that I think of deleting old project files.
Is it possible to tag a project originators email address and automate an email, say, one year after a project has been posted. A link could be sent to the project files allowing the poster to quickly clear out his old files. just a thought.
Otherwise, I have found the site to work well as is. 65MB has never been a limitation when compressing to ape. If someone really requires more than you offer for free, maybe they can purchase their own account from 1and1 ( $5 bucks a month guys) - through your affiliate link, of course