Just to hammer a point made earlier, NEVER do more than you are trained to do, regardless of good samaritan laws, you can easily do more harm than good. The only time you should ever consider removing someone from an automobile after an accident is if you believe they are more likely to sustain a life threatening injury by remaining in the vehicle - i.e. the vehicle is on fire - otherwise do what you can to support life with them in place.
I would say yes and no. I would agree totally, that if a victim is breathing and no life threatening conditions exist such as fire or a leaking fuel tank, you should wait for Emergency Services. However, if a patient is not breathing, has no pulse and the need for CPR has been established, you should as carefully as possible, maintaining some time of C-spine control, get them out of the vehicle ASAP. Remember the adage “life over limb”; if CPR is required leaving them in place is only going to result in death. Effective CPR cannot be readily performed while they are in the vehicle.
Pete