If the system has to deallocate time channels for other vehicles to use, it loses bandwidth, proportional to the number of vehicles in the vicinity.
Sharing the data between vehicles is possible, however, it invokes geographical/networking problems, such as how to partition the acquisition, how to synchronize the acquisition and how to share it, including the necessary bandwidth, which I'm sure is quite high.
As soon as multiple vehicles sharing data enters the picture, security must also get factored in. Besides the link control concerns, the system will be sensitive to jamming with that much multiplexed sampling taking place.
PP is correct in hinting that the leap to multiple self-driving vehicles from one self-driving vehicle will be large indeed.