Though there are few truly vital reasons to leave LA's urban soup for San Diego's relative towniness, there are a few compelling ones. Most of them involve fantastic CaliMex food, the insane Tijuana border--for which I had neither the stones nor the time to visit, instead choosing to guide my lovely female companions to relative safety/sanity--and NFL football, SoCal-style. But if you're a student of architecture, conquistadors, or just like the beach, it's worth a look. But first a little history...
The area was first explored by Spanish explorer Sebastian Vizcaino in 1602 and named for a Spanish saint, San Diego de Alcalá. In 1769, a group of Spanish missionaries established a permanent colony on a site now known as "Old Town" San Diego. Later, the colony transformed into a military outpost, displacing the missionaries a few miles to the east, and was the location of a few small skirmishes between Spanish soliders and the indigenous Native American tribe, the Kumeyaay. Mexico gained indepedence from Spain in 1821 and San Diego progressed under Mexican jurisdiction until the resolution of the Mexican-American War in 1850 (known as the Treaty of Guadalupe Hidalgo) ceded the city to the U.S.