From the way each of the deliveries / diversions / etc was described, I thought that maybe completing them would have some impact on the world - that since EA is coming in later to the open world genre, maybe they could do stuff differently.
Something as simple as an allegiance meter would get me more interested in doing the extra activities. Doesn't have to impact the overall story (ie. Mr Kruger still wants to hunt you down), just the world when you're running around outside a main mission.