How about sneaking/invisibility into the middle of the group of enemies and using earthquake while the rest of your party is not in the battle?
Or engaging first and then using the spell?
Everything has its use.
That said, I haven't actually got to the point where I can cast the spell, but there are many different playstyles, and different spells have different uses.
I'd consider smokescreen, firefly and ice wall to be amazing spells for example. I rarely use them, but when either the situation demands their use or I create a situation in which their use is good, they're amazing.
It's just finding the use and determining if it is a worthy use of your AP to use a spell or not.
