Just a heads up for SDCC, the wife and I just got back from a weekened in San Diego & La Jolla (we drove down) and the homeless were out in force in the Gaslamp Quarter. We go down a couple times a year and I don't think it has ever been this 'bad' (sorry, can't think of a better word).
We parked on the Northern corner of 3rd/4th by Sevilla and there was a group of 15+ in the parking lot screaming at each other, pretending to play basketball with a wall, talking to themselves, and just doing crazy stuff. One guy walked right by us as we were getting the parking receipt, pulled off his shirt, then started doing leg lifts & push-ups on a concrete block.

We also saw open drug deals and too many people sleeping on the ground to count.
We go to San Diego a few times a year but we definitely did not feel safe as it started getting dark. On a side note, the Pussycat Dolls were doing some outdoor concert by the Hard Rock Cafe, so we had VERY loud, obnoxious music to hear.