And that is the fact that stacking Fans increases your Max STARBITS gain from missions.
When you first start out, it is so that every 50 Fans gained increases the MAX STARBITS you get from missions by 1 point. Now, that doesn't look much, but...
That 1 Max STARBITS reward every 50 Fans get you is more prominent in shorter missions as they already have a few STARBITS as a reward.
After gaining 50 Fans, the rewards increase by +1:
There's a certain point (in the number of fans), after which doing shorter missions becomes ENTIRELY more profitable. I'll leave the experiments to you as the answer can vary from person to person depending on their investment in the game - especially the daily time put into it.