Are they useless? What do they do? I mean, the storm miracle is a combo of rain and wind, but they're both pretty much useless after you've passed the missions you need them for. Ya know, not useless, but not worth using. And the earthquake doesn't seem to have any purpose at all, though I've only tried it once or twice.
Do they have much purpose? You just kinda get them thrown at you at the end of the game as if it was an idea to have more miracles but they didn't really fit...

Ohhh, no wonder I found him so hard
Yeah but wind and rain are useless. I mean, rain is only needed for the desert crossing, only once. And wind helps long range attacks, but it means you can only attack with Yaripons so it's just not worth it. They're the only attacks that get significant gain from wind.

I don't even think you face many Zigotans, if any after you get the earthquake miracle...It's like the end of the game, and you can't replay the Zigotan missions...

Do some other missions to get better weapons and guys. That's basically all you can do.