Unfortunately, Avis doesn't guarantee the car you reserve unless it's a "cool car". Avis also won't give you a better shot at a car depending on the EXAMPLE that's listed for that car class. In reality, the CTS used to be the Avis example for Luxury and Expedia just hasn't modified their page yet. And Avis is dropping the Cadillacs from the fleet very quickly and replacing them with other Lux cars so your shot at a CTS is very slim, IMO. After you book the reservation, you can call the station a few days out and ask that your reservation be noted that you want a CTS but that's a far cry from actually getting one.

As for the insurance, that really depends base upon your personal needs. Some credit cards or your personal insurance policy will cover what you need and then the Avis options aren't necessary. If you don't have other insurance, then it's highly recommended so you don't damage the car (and/or injure another car/driver and yourself) and get stuck with a HUGE bill. Just beware that there are multiple kinds of coverage and you get what you want/need.