Many of the subjects of Streetsblog's "criminal mischief" (defaced or obscured plates) are vehicles displaying NYPD parking permits. This problem won't get solved until someone besides the police is tasked with fixing it, at least in NYC.
Separation of powers is the key to a functioning government, and should be for the policing arm of the executive. Peace officers should obviously be tasked with the day-to-day of the policing.
However, enforcement of policing rules (within the executive branch) should come from a separate meta-police force based in the judicial branch, confirmed (and impeached/removed) by the legislative branch. This meta-police force would have full policing powers, but their jurisdiction would only extend to peace officers and members of the policing or district attorney's hierarchy.
Basically, you could rob a bank in front of these meta-police, and they could do nothing, but they could fully investigate a police officer accused of intentionally obscuring their plates, or unequally enforcing the law against folks with police benevolent society cards.
The idea that the executive branch, alone, can act, to me, is crazy. The Judicial branch is supposed to care about justice. They should have a limited arm to act much like the legislative branch has a limited arm to enforce subpoenas without the executive.