What it really boils down to, as with all laws, is what the cop-on-the-street is instructed to enforce.

The City Attorney can blow his horn all he likes, but if a cop doesn't write a ticket, he'll be golfing more then lawyering.

That said, the determining factor in all of this will most likely me the Mayor of Denver. He will either instruct the Cheif of Police to follow the will of the voters, or not.

You will always run the risk of being pulled over by Highway Patrol / State Cops, in which case, no city ordinance in the world is going to stop them from enforcing CO state laws first and foremost.

Even in CA, until very recently, if you purchased Medical Pot from a club and then transported it on a highway, you ran the risk of being stopped by the Highway Patrol who were instructed to confiscate it. This was because the state was affraid of being criminally liable under federal law, but they have since nutted up and stopped.