Alright, a few quick hints:
First, Spellcraft DCs: try to find ways to lower DCs either by adding XP cost, getting help, etc.
Second, buy (or craft) custom magic items to boost your spellcraft... alot.
Spell resistance: prepare the spell Assay Resistance from the Spell Compendium. It is your friend, your good friend.
Touch attacks: Time to boost your Dex, it would appear. Also, Quickened True Strike. Alternative: have a friend, Summoned Monster, Bigby's Hand, or Tentacles grapple 'em to knock down their touch AC. Also, if they don't know where you are (Improved Invisibility), they lose their Dex to AC. That might help.
Save DCs: Well, if your ninth level spells have a 28 DC, have you Wish-boosted/tomed/Magic Itemed your Int up as far as possible?
15 base +5 levels +6 Headband +4 Wishboost/tome=30, which should be a DC 29 ninth level spell...
Also, negative energy makes it harder for foes to make saving throws... Enervation and the like, once you get past SR and touch AC dish out hefty penalties on saves after awhile... and the only save that they allow is against it being permanent.

My little hints, some of which derive from my one Epic-level campaign, more of which derive from my brother's complaints about an Epic Psion.