I'd suggest somewhere in the Anaheim area since it's in the center of SoCal. It would be pretty easy to get to for people in SD and in the IE areas. I'm sure the restaurants in west LA are nice but they are a long drive for the people in San Diego.
I also think that Anaheim probably has lots of facilities that could host an event like this because they see conventions all the time.
"There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order."
"The shotgun is an art, the rifle is a science, the pistol, a craft."