Currently a large portion of the game is focused around gaining XP through eating better food and living in better homes, but XP does only one thing: provide you with stars.
This very often stops being an incentive by the time high XP items are available, as people typically have more than enough to do with just 3 or 4 stars.
If XP were used for more general gameplay, it would increase the importance of this mechanic and make better food and housing desirable to more people and for the entirety of the game cycle.
One example of how this might be done is an XP upkeep for running workbenches (as well as their respective upgrades), so you are only able to have so many workbenches and upgrades in operation at a time according to how much XP bonus you have.