Hirelings.
Seriously, the one hireling keeps getting her journal read by a competitor that tries to get your business. In one mail, the competitor says that you were attacked by bandits hired by them. Making that a quest occurrence would be so much better than a random reference in a mail when you have not even seen a bandit in weeks.
Also, sometimes the hireling run into an issue and need help. I would love to provide the help in a quest. Or even pay/tip the hireling every once in a while. Perhaps leading to a specialized message.
One of the hirelings mentions that they provide components to you simply because of the prestige associated with working for you. A good quest would include doubters - and you show up to prove they work for you. Or just destroying someone that is interfering with their component collection. So... many... possibilities...
At any rate, more interaction with hirelings through quests would add an incredible dimension to the story lines.