This is what a CO state trooper told me like a month or so back. He said unless the the plate is mounted on the front plate mounting bracket provided with the car (or how it was intended to be mounted by the manufacturer) a cop can give you a ticket for not having a front plate. So all you peeps that think you're getting away with putting the front plate on your dash, or wired to a lower grille...think again. The cops probably don't care enough to pull you over for just that. He also said that a plate on the dash draws attention to the fact that you think you are cool and will likely cause a cop to look for something more to pull you over. So, as you can see, having just a europlate on the front will probably cause you to get pulled over more than having no plate at all.
Also, CSPD does have a quota of tickets to meet. It is 30 per month per cop. So, that's about 1 per day, but if a cop were to miss a week for being sick, or have a 2 week vacation, that means they gotta give out more tickets. Just some food for thought.