There are for sure cost efficiencies with group packages, but I would argue it's largely because of all the equipment driving them - remember for the most part that too has to be standardized. If you think about it, that's where stations are finding savings. FOX with Chyron, NBC and ABC with Ross, etc.
I guess my point is that if you're doing a group package right, you're finding ways to affird localization opportunities so it doesn't get stolid or boring. Keep the design language consistent across the group, but having local flavors that can sometimes go beyond just swapping a photo or video in the open -- maybe a color palette change like KYW, for example - at least shows you have some boots on the ground paying attention. I agree; most probably don't care if stations share a lower third. But I bet if a station's group main opens can showcase the market and demonstrate some care and consideration into it, it could go a long way.
That's what makes me really interested to see how WPVI interprets the ABC group package. If anyone has latitude to distill what is a fairly formulaic open down to its core design language and keep the heart of what's made their locally grown anthem open successful for, what, 50 years now--it's them.