In regards to the High Arcana, I get 6 spells/level/day as a 20th effective level sorc, so it won't kill me to lose a couple of high level spells. Sooo
Arcane Fire: Nice. supernatural ability bypasses SR, does decent damage, 6d6-14d6 depending on the spell slot I burn
Arcane Reach: Doesn't seem especially useful to me. Most touch spells that do damage are lower level, are they not? Most higher level ones are ranged touch.
Mastery of Counterspelling: Would this not stack really well with the Incantatrix levels?
Mastery of Elements: Always good to be able to pick the right energy for the job. Got a fireball, but you're figthing an outsider with fire resistance? Make it an iceball instead.
Mastery of Shaping: With my habits of firing spells into areas near other characters, my fellow players should love this one. Nothing like being in the middle of a bunch of baddies when your MU decides to blast them all with a fireball or some such. Now you can have the spell go around them
Spell Power +1, +2, +3: Get through that SR and increase the saves. All good and stackable.
Spell-Like Ability: Now, never be without your favorite spell. Sure you lose a spell slot to power it, but now you can have that sextuple empowered fireball without the wait for a metamagiced feat. I'm not so sure that this is terribly useful for a sorcerer since he doesn't have to prepare spells anyways.
Of these, I'm leaning towards Spell Power +2 and +3, Arcane Fire, and then two of shaping, elements and counterspelling, probably shaping and elements since I've never done any counterspelling. That would cost me 2 9th level slots, 1 8th level, 1 7th level, and 1 6th level slot.
One of my bigest concerns is getting the 5 schools of spells from 5th to 7th level. At 15th level, I only have four 5th, three 6th, and two 7th level spells. Also, what schools tend to not hurt too bad to lose? I considered Necro, but then you lose most of your save or die spells. I'm leaning towards Enchatment or Illusion possibly.