Alaks,
I have now completed my upgrade process and can confirm that Rajesh is accurate when he stats that a catalog upgraded by version x of admin studio can only be accessed adminstudio version >= x
If any InstallShield staff happen to be reading, please note that I would have appreciated knowing that 1) A database upgrade is required during the process of installing the value pack, and 2) that, as a consequence, all my developer workstations have to be upgraded at the same time if they wish to continue using the same shared catalog. If this information is documented somewhere and I've missed it, I apologise for unfairly criticising you, but I did have a look around and didn't see any warnings to this effect.
Anyway, all resolved now, so I'll get back to my packaging. 😉