I have next to no Gems right now since I have used them for Equipment storage and Girl storage expansions. Also they are very useful for getting new girls but only if you go about it the right way. We have proven in the past that buying something with NGold seems to increase the drop rate of 5*+ girls from Gem gatcha right after the fact, 100NG yolo pulls seem to be enough. I have also noticed that 5*+ droprates seem to be higher right after a new gatcha has been released (first 24 hours or so), but that one could just be RNG and Luck on my part.