Cold is pretty much the win.
Three runes of AoE cold, and you have all the time you need, and the setup, for lightning+arcane. Only cold resistant spell mobs or big boss mobs are invulnerable to it.
So, cold spray = handy for freakout moments of being surrounded.
Cold aoe = bread and butter of making the game easy. Run through mobs, bomb them with cold, turn around, nuke them.
Cold lightning = slows and deals extra damage for being wet. A win/win.
Cold stone = Basically a cold fireball, that drops a cold patch where it hits. Great for aiming at oncoming waves, and stopping the whole wave COLD in its tracks. Getting out of the effect of it is as easy as one fire on yourself.
Cold/Lightning/Arcane = Game-ender on anything but bosses. A slow, extra lightning damage beam, and explosion on death. Paralyzes most mobs in their tracks.
Cold + Shield = Cold barrier, protective curtain that slows anything that gets near you.
Cold + Steam? = Haven't tried. Perhaps it leads to freezing solid quicker.
---
I agree Fire seems to be the big loser. The DoT is weak, it takes a lot of fire damage for an enemy to panic, and it cancels cold, wet and freezing, the three most useful elemental effects. I struggle to find a reason or a desire to use it ever, other than to blow up goblin bomb carriers.
I think Earth is under-rated. Its AoE might be crap, but a straight 5 boulder max charge will decimate everything in its path.
I find myself never using any of the extra magics besides haste. None I've encountered seem more than situationally useful.
There's also never really an excuse to die from HP loss if you're not grabbed. You can load up heals and heal yourself while flying through the air. Spamming heals, at least when you're got basic HPs and such, takes about 1 second and you're full.