Luckily, I've found the ring of satiation early on, it helps A TON when playing heavy caster.
Just got the serpentine rune (in Snake Pit, I skipped killing Lumia, though). Now, realized I that I've under/overestimated few things about my char:
Sif. I knew that gift spellbooks are good. But channel energy is quite weaker than I though (gives a very little boost in MP, though is sometimes enough to get you out of a rough spot), but more importantly, Forgot Spell is way more useful that I imagined. Coupled with the huge amount of spellbooks, it basically allows you to adapt to any branch, as long as you diversify your spell schools - you just forget some spells and learn the needed ones. Need crowd control for Orc ? Get Meph Cloud and Fireball. Need poison for Spiders? Get Poison Cloud and Pois Arrow. Going Snake next? Forget poison and learn fire/air spells. Shoals? Repel/Deflect Missiles etc etc.
Black Draconian. I died enough times from Pikel's or Wraith's elec weapons and from elec eels (I even made them travel exclusive by default) to know how much rElec helps. And I did knew that that breath weapon isn't all that good, as even though it is powerful, esp later, it is just too random to be reliable. But I had NO IDEA how much at will, perma-flying helps. I basically beat Snake cuz on S:5, near the final lair where there were dozens of enemies, there was also a pool of lava. I basically cleared it but triggering aggro on few of them, flying into lava, and than spam them with Ice Clouds and various Bolts, while they cannot reach me. It was marvelous!
tl;dr - Sif's Forgot Spell and at-will permanent flying are both awesome.