the amount of the ticket could increase and if you fail to pay a civil matter the court could issue a civil warrant, additionally you could lose your right to operate a motor vehicle for unpaid tickets after a while.
If the city is mailing you tickets and now appearing at your door and you do not respond, you run the risk of being cited for Failure to Appear, which in most jurisdictions is a misdemeanor. However, if you are arrested on a warrant for FTA you will go to jail until either the original fine and the FTA fine is paid or you post bond and seek to fight the citation. You can try to challenge the consitutionality of the cameras- some have been successful, but you need to determine whether that measure is worth it. Nevertheless, the city will not just forget about you. A warrant will be issued, and sooner or later, they'll find you and it will likely be an inconvenient time.
This ticket is not going away by your ignoring it. Your driving privileges could possibly be effected, Contact an AZ traffic attorney to deal with this.