There are some noticable differences between the operation of the two systems. A few of the commands are different.
I haven't used them enough to see, but honestly I am not the right person to ask anyway. I rarely have problems with VR on any of them because I practice the commands quite often while working on them. I wish I could say I know for a fact that they have revised the VR software but GM hasn't told us anything like that. I'll go see if I can find a bulletin or something to that effect.
It's sad I know but this is all they tell us.
If the OnStar system properly responds to any command, the hardware is assumed good and the customer should be directed to the description and operational characteristics in published Service Information (SI) and the Owners Manual. They may also be directed to contact OnStar and be connected with the voice recognition group for assistance with system operation and tips
As far as the benefit of updgrading:
The deal is, as I understand it that next year the FCC is practically forcing all transmission to a digital format. Analog is about to become a thing of the past. Now I am not sure how fast this will take place but basically everyone is already switching to digital equipment, like cell phones. As it stands, companies like cellular providers are currently maintaining networks for both analog and digital customers. Next year if the FCC starts revoking analog licenses and companies decide they only want to maintain one network instead of two (and why wouldn't they) everything will switch to digital and those with analog systems will be left out in the cold. That means if you don't have a dual mode OnStar unit that will work on a digital network, you won't have any service because no one will be providing it, there will be no network to handle your signal.
Basically no digital upgrade = no service in the future. Strangely OnStar has chosen not to include any models prior to 2003 in this upgrade plan. I guess they figure you can either buy a new car or if you have a car 3 years old or older you just don't get OnStar anymore.
Now, that is the way I understand it. There could be some holes in there big enough to drive a truck through so if someone has done more research I am all ears. I don't have time to hunt down the information to verify all of that so take it with a grain of salt. If I find out anything different I'll let you all know.