A richer set of commands? Like what? Faster or more accurate movements?
Yes. For example spline was created later on. Spline motion usually is faster and has a higher precision in path guided motions.
Also VKRCs usually are not equipped with absolute accuracy because VW never uses and therefore never orders it from KUKA. For KRC4 this might be available and increases robot accuracy. So you should check whether the system you are buying has the absolute accuracy package which is no general package that can be installed on any robot but is a set of specially defined machine data exactly made for a specific robot (a single serial number) to make it high precision. Btw. the HA in the robot name states High Accuracy and usually then comes with the absolute accuracy package. Also some other mechanical parts of HA robots are chosen special to allow this higher accuracy.
Also the programming interface for VKRC and KRC are very different. Even though in the end both systems run with KRL code. But getting this externally generated KRL code to run on a VKRC is more difficult than on a KRC. I can not say for sure whether Grasshopper even supports VKRC. Interfaces of VKRC are very much pimped to exactly fit into VW plants and VW way of thinking. In general KRC is a more open and as most people say simpler to handle and flexible system. Even though you plan not to do much on the robot side without touching and at least having a small grasp of the robot system will not work.
Also no matter what machine you have eventually something will get damaged. Spare parts for KRC4 are still available. For VKRC2 it might get difficult to get them and then they also are already old and might not run as long as well.
Fubini