We've checked into airports several hours before our flight. You might want to check with the airline you want to use.
I've heard that Seaport Village in San Diego is a nice place to spend some time. I haven't been there personally but heard good things about the shops there. It's only 10-15 minutes from the airport.
Their website says the following: Four miles of meandering cobblestone pathways bordered by ponds, lakes, fountains and colorful, lush landscaping. Quarter mile boardwalk along the San Diego Bay. http://www.seaportvillage.com