It really depends. I occasionally use FGs for Stamina refills for the Manyu daily, but then, my maximum stamina is 370, which means I can do the 80-stamina map four times for one Flower Gem. Shortly after I passed 320 maximum stamina, we got the "bonus chest" on the daily maps, and that was just enough for me to push "not worth it" over to "totally worth it".
But, I personally wouldn't do it if:
-I had less than 320 Max Stamina (so couldn't do 4 runs on 1 FG)
-The "bonus chest" didn't happen (bug or not, it made using FGs for stamina worth it for me)
-I couldn't beat the 80 Stamina maps (Less or no chance at lvl 100 Manyus/Dragons make the lower maps useless to me)