I would like to access the Sitecore API from within a command line tool (with a goal of exporting some information about users in the database), however I haven\'t been able to
This may be possible using App.Config (I cannot confirm or deny) but you will have a much easier time doing this by web service. Likely easiest would be to create a custom web service with the logic you need, and use a CLI to call/trigger the service.