When I was living in Wisconsin, I was pulled over once in 10 years of not running a front plate. I was a block from my place in Milwaukee and got lit up. The cop comes over to me and says, "You know you are supposed to have a front plate." I reach behind the passenger seat, into the map pocket (looking back this might have not been the greatest of moves), and pull out the plate. He says, "Have a nice day." And guess what... I did have a nice day.
Living in California now, I wouldn't even try to not run a front plate unless you have out of state plates and then they can't do anything about it. Can't enforce another states law.