There is a website here for Car Shows.  If the portal users are all local, then it would be easy to send an email to all portal users.  As the coverage area expands to different states, the Forums module can be used to send out emails to interested people in different states - when people subscribe to different Forum topics in the Forums module.  Similarly, if event notification were to be added to DNNEvents, I would prefer it to occur BY CATEGORY where category would be CarShows-PA and CarShows-TX etc. 
In a Master - Slave situation, where a Master displays all Car Shows in different states, and a Slave Events module is setup on a separate page for each Car Club, then the individual Club's Events Administrator could add & edit all public events for their club, without affecting the entries by other Clubs.
Again, it is probable that a separate Mailing List be used to notify only their own Club members of the happenings, or that club's individual members should join that club's Forums section... which can notify only their own members.
Yes it should also be possible to someone to receive email notifications from the Master Module, such as New Reporters, however if many events are posted in areas they're not interested in, will quickly cause a problem when that person emails the Events Moderators asking to be removed from the mailing list... the problem then is to find where the person subscribed. 
In a small scenario, emails from the Events Module will work as anticipated.  In a large scenario, it could get out of hand quickly.  It is probably better to use other tools to manage email notifications.
One way of thinking may be to setup a complete separate Portal under the DNN instance for each participating group - that way people in TX (Texas) can join the TX portal, join the TX Forums, and get notified of the events occuring in TX.
!  Which type of portal is recommended? A Child portal or a Parent Portal? (so that if the Texas group wants to map to a Domain Name, they could.)

BarryZ