[Brian]

OmniFocus does create duplicates of your repeating Actions, but the "Archive Old Data" feature should keep things from getting out of control. Each month (or however frequently you prefer), just use that command on whichever Mac you want the archive database to live on.

I have several actions that repeat twice a day, and after using OmniFocus in this manner since 2007, my database is still less than a megabyte in size.