I think you missed my point completely, and therefore simply whitewashed everything.
Please explain the math behind your "1% chance of receiving an intact transmission due to noise and interference" statement. You can't make that claim without laying down some facts. I've pulled down TPMS sensor traffic (that has a nominal range of 20') at distances of over 300' with the use of a simple HDTV antenna and a $20 RTL-SDR, and I did it in sprawling suburban traffic density, not out in the boonies somewhere. It's actually way easier than you think.
Forget about identifiers for a second. Directional antennas can provide significant rejection of off-axis signal, while boosting on-axis SNR. If you are listening in a specific direction using a steerable antenna or a phased array, and if (like TFA states) the target vehicle is transmitting up to 10x/sec, I can string together a series of broadcasts to determine a trajectory. It doesn't matter if the target vehicle switches identifiers, because I'm not talking about tracking by identifier. I'm saying that at 10x/sec the resolution is tight enough that under traditional Newtonian physics, I can deduce which packets belong to the target car. Basic trigonometry can provide a solution from my location to the target's anticipated location to keep the antenna pointed in the right direction. This is totally possible, and it can be done with probably less than $2000. A laptop, a high end SDR and a small steerable yagi should be enough to get you there. That's cheaper than the infrared goggles you mention, let alone the helicopter, and requires no training for a surveillance team.
About encryption: I'm not suggesting the entire protocol has to be compromised. The transmitting car can't know who is going to receive the message, and negotiating an encrypted connection takes too long (think closure rate of two vehicles traveling head on at 70 mph). Some messages may well be encrypted, but the secret must be pre-shared among manufacturers if any vehicle is to decrypt any other vehicle's traffic. Therefore, it's only a matter of time before keys are leaked, and abused... but with the cops, it won't even be a leak: the cops will just ask for the keys and get it. Once the cops have it, someone will figure out a way to steal it from them and voila! But more importantly, the unencrypted data provides enough to do what I'm talking about.
You are right though... the cops will probably just put an antenna on every streetlight just like they want to do with video cameras... then they can track you from the comfort of their multi-million dollar control center downtown. But what you are wrong about is that it is not really going to change anything. That's what they said about social security numbers. In fact it will change a lot of things. Anything that is made easier, is made easier for the good guys as well as the bad guys. If you don't see the opportunity here, then your'e intentionally ignoring it. It only takes one or two bad eggs... every police organization has the potential to have someone who abuses their power. And every new technology is exploitable, because the people who create them are not half as clever as those who wish to profit from it. Whether it's the cops or the criminals or both, this tech will do some good, and it will also do some harm.