I look forward to seeing other approaches to this, but here's what I do. I have a folder I have titled "Project Templates" in which I put in various projects that are repeated, but not at regular intervals (Class Planning, Travel, Conferences, etc.). I put all of these projects on hold so they don't show up regularly, but when it comes time to use them, I copy the project, make the copy an active project, drag it to the appropriate folder and make any adjustments I need to.
Curt Clifton has an applescript which you can use to plug in titles, start dates, etc. that is really handy for conferences (you put placeholders in your template then "Populate" the template using his script. It creates it's own copy with the variables inserted, which I then place in the appropriate active folder. See
http://www.rose-hulman.edu/~clifton/software.html for a list of his scripts.
Hope this helps.