Galaxy GB is not only FP producing. On palaces, it also produces goods. If you have a level 52 BG and can collect 12 palaces, that is ~7 palaces daily that will be doubled. In other words, 35 refined goods + 35 FP.
The only other GBs that give refined goods are DT (luck-based unless you aid manually), Chateau (no FP boost), Seed Vault (no FP boost), and V1 (dependent on being able to plunder something from desirable age).
Also worth noting that Galaxy is one of only 2 GB where you have control over what type of goods you receive. For example, you can get extra Arctic goods while in OF. (other GB is DT)
And lastly, it is by far the laziest option out of all of the above GBs listed - you merely need to log in and collect - don't need to aid, don't need to battle/plunder, and don't need to loop quest.
At any rate, this GB is not a priority for everyone. It depends on the kind of city you have and what you've already built.
I've already leveled every FP GB to 75+ so this makes sense to level next.