The question of the type of vehicle driven on-duty by policemen should be an administrative decision made the Chief of Police. They should be allowed to drive any make, including Maserati, that can be justified in the department's budget. The fact that is that many departments have put expensive cars into service because they were obtained in drug raids and property forfeitures.
No, police are not entitled to drive more expensive, luxurious cars on the job. Police officers are actually public servants who operate and are compensated fully from money from the taxpayers. It is important for governments to operate frugally and not spend frivolously since they are spending tax payer money.
Because police cars are provided and paid for by taxes, costs should be kept as low as possible. There is no need for expensive police cars and it would be unfair to expect tax payers to fund expansive cars such as a Maserati when most people don't drive that type of car.
There's no reason for police to be allocating valuable money and resources to drive luxury brand vehicles on the job. There is no necessity for any police officers of any standing to be securing these sorts of vehicles for other reasons than vanity, and it is that vanity that makes people distrust the police.
No, police should not be entitled to drive, on the job, more expensive and luxurious cars, because there is no need for them to have fancier cars. Law enforcement only needs fleet cars to get the job done. They also often ruin cars, and it is better for the taxpayers if they are not ruining expensive cars on a regular basis.