I don't get it--I honestly have no problem paying $22.29/yr for this cool system, and I'll probably just end up doing that I guess, but I just don't get why I am now apparently being required to do it with no big systems or anything saved. Do I have too many modules saved in "My Modules"? I can't imagine so...

However, any time I click on one I'm brought to the Unicorn sign-up page. What am I not getting about this?

Hey man, you can only save modules to "My Modules" if you have a Unicorn account. It is a feature of the upgrade. If you once had the Unicorn account and saved some stuff to My Modules then you get to keep that, but you can't add more until you re-subscribe.

Trying to make it a bit more clearer:
Every one can add modules to My modules, but you need a Unicorn account to add modules from the My module page to your rack.
Clicking on a module in the All modules tab redirects to the module detail page while clicking on a module in the My modules tab adds that module to your rack. If you don't have the Unicorn account you will be redirected to the order page.

... and thanks for supporting!