I think the plugin button should be used as the method for presenting the user with info such as this:
current_date<event_date = "Registration Not Yet Open"
current_date>event_date = "Registration Closed"
user already registered = "Already Registered - click to edit or cancel" then this takes you to the edit page.
Right now it just says "Register Now" which fools everyone. And everyone goes back to the event anyway to try and edit or cancel their registration (thy never go to the menu link for this) so making the plugin change to the "Already Registered - click to edit or cancel" would really be helpful.