I must be lucky--- I've lived in CA all but a few years of my life, and I haven't run a front plate on any of my cars since I started driving! Despite this, not once have I been pulled over for a missing plate; then again, I've only had two tickets in the last 25 years (one was on my motorcycle) and even then during the one stop nothing was said. Currently all five of my cars don't have 'em, including my company car. I would be more worried about too dark of tint on the side wondows than anything else.
Just my $0.02.
PS: John Hine Pontiac in San Diego was smart: they left my GTO's front plate installation kit in the trunk-- where it belongs.