So this Earthquake spell thing...

[SailHawk]

Upgrade to do more damage to buildings. Works great if you can fit an inferno in it to soften it up a little. A little bonus if it is close to the walls your opening.

[TrapezoidSteve]

Upgrading it could reduce number of spells required for same result though. If you can get it down to 3 spells you'd be much better off.

It doesn't though. It takes 4 EQ spells of any level to destroy any level wall. And to answer the OP, I would say don't upgrade it just yet. There's a good chance level 1s will be nerfed in the future, but as of now there is no good reason to upgrade them.