If you do something like this with 2 buttons.

Arcane Spells
Code:
/castsequence reset=combat/6 moonfire, insect swarm, starfire, starfire, starfire, starfire, starfire, starfire, starfire, starfire
/cast Starsurge
Nature Spells
Code:
/castsequence reset=combat/6 insect swarm, wrath, wrath, wrath, wrath, wrath, wrath,wrath, moonfire
/cast Starsurge
You can just alternate... an idea i was also toying around with is a keymap that just strafes left on press and strafe right on release and just moonfire spam and cast starsurge when it's instant cast