The Birch Acquarium hosts events in the foyer and is a nice venue. Guests can wander around in the exhibits and have drinks on the outdoor patio. The only downside is that it is echo-y b/c of all the tile and hard surfaces.
May want to call Addison in Del Mar. They have large private rooms and the largest may be able to fit your party.
Nine-Ten is adjacent to the Grande Colonial Hotel, as is Kitchen 1540 at L'Auberge in Del Mar. Both restaurants may be able to "cater" in the larger hotel ballrooms.
For a group that size, and with that budget, you're pretty much looking at the same venues that would be used for weddings.
I would try the private room at the Prado. Great location, decent food, etc.
The Museum of Contemporary Art in La Jolla (and downtown as well, i think) does private group functions too.