One-time demographic questionnaire that we all have access to
Have Turkers take a fairly comprehensive demographic questionnaire once and consent to letting all future researchers see it. That way we don't need to ask them for their gender/age/income every time we survey them. Asking these things can activate psychological processes that can affect results (see: research on priming) so it would be great if we could ask them less frequently.
This site does some of what you are requesting, though maybe not as involved.