you are right when it comes to them wanting you to upgrade membership to get support. Recently on their forums, you see most of the "free" support being asked to upgrade to get better support.
They claim you can get free support, but @robert62 on almost all threads recently has been urging people to upgrade. So, free support isn't available here as @robert62 has made the requirement for you to go to their site and ask for support there. Once there, you will probably be asked to upgrade.
I wouldn't mention it, but Simon, the Dev. has said on here before that they don't try to make you upgrade. I think things have changed a little. But don't take my word for it. Try it..
If WP Symposium hasn't changed the way it handles users (I haven't tried lately), WP Symposium should inherit all users from the WP Database. You shouldn't have to import them as they are already there.