For now I prefer to keep left over gems to do some fun pull from time to time.

40 gems for 1 dressbloom is still a lot forme, compare to dressbloom that they sell with NG.
I don't remember how much but I think it's 3000 NG?
And with those step-up deal that have dressbloom with it look more beneficial I think.
In the end it just my POV.