What's about feedback from your downloader ? are they complain or they tend to not download your file ?
I think most people cant be bothered doing surveys and i don't blame them. The best way to look at it is to think "What would I do"? And personally, if it was me, I would close it and find what I want somewhere else.
Most of them are crap. If you do have super super...... great stuff and folks are willing to do a survey, once they have done one your content will still be restricted because a) the are not in a suiting country b)in order for them to pay you big bux they have to scamm your visitor into doing more than one c) technical errors. Some firms vanish into thin air as soon as they have done well for themselves. And honestly most of the time someone always finds a way to get to your content without surveys and whatnot and is willing to share the flaws of the system with others on the web. Mate, piece of advice save your time, save your nerves and don't piss of your visitors - stay on the pay per upload scheme.