Beyond Flashpoints/Operations.
1. Bonus XP from bonus missions
Just for bonus and it makes doing bonuses in a full group well worth it. Since you get your completion exp + half of each persons completion. So in your example would be 1500 + 750 +750 +750.
This assumes a full player group, not a mix of players + companions filling the empty slots. Nice that they do this though
2. In FP's different choices each run through actually can vary how the run goes, rather than zerg boss 1, zerg boss 2 etc.
Anymore?