And what do you do with them? I've got 150k atm but I'm debating whether until more heros arrive then role the whole lot. I just need the fox, so I think I'm going to wait until I need 5 new heros then go for it. I've rolled 80k before and got nothing from it
This is good strategy.
Rolling gems for one new hero is not that good, since you will never be sure if you will get it. It is better when you will search for few, since theoretically you have higher chance of finding one from few than only one.
I'm also saving gems, but I'm nowhere near you, barely half of what you have, but I'm always saving 30k gems just in case if any good spending gems event will show up. This way i was able to participate first Egg Hatch-A-Thorn event where you could pick more gems than you used, and i was able to max fennec fairy quickly.