My concern with #1 is that even if there is an increase in reward, it doesn't increase collaboration. Some folks will still exclude Stage 4 Prime holders based on the composition of their group. We have to think many months and years into the future with the solution to this problem.
I would recommend that Enraged Bosses are a separate selection when entering Sortie, if someone has a Stage 4 or Stage 5 Weapon. Also, I like the idea of adding 10-50% additional Gallimaufry when a party has 2-6 Stage 4 (or Stage 5!) weapons.
This would have the added effect of subsequent Prime Weapons earning Gallimaufry at a faster rate. In my opinion, this will increase collaboration and improve player retention.