This is cool and it isn't too simple. I agree though that it needs some optional text boxes to enter a title, location, date, and time. Maybe keep the current simplicity but:

-Make a logo for the top right corner with your branding

-Allow users to edit the Title at the top of the page to whatever the event title is

-Make the subtitle editable so people can add extra info like their name or phone number

-Add a calendar to the right side so people can optionally add a date and time

-Add a google map to the right side so people can optionally add an address

-Clarify that those are both options and if they aren't configured then hide them from the invite page

-Add an optional email box to the generation page so you can receive a secret admin link in order to change the details later

-Add an email box to the invite page (also optional) so people can sign up to be notified in case of a change in time or cancellation

-Ajaxify these options so they're quick to edit. See: Google Notebook for how you should make the titles and other things editable

Okay that turned out to be a lot more changes than I anticipated.