Kaleidoscopic Doom is indeed awesome simply because all the relevant opponents are buffed to high heavens. That said, if you are an Incantatrix, I don't see you fitting 7 levels of Initiate without weakening your character. And yeah, Dispelling is the key; it penetrates the commonly available means of defense (I don't think Spell Mantles exist within WoTC 3.5 rules; either way, they should collapse under Greater Dispel Magics or Disjunctions if all else fails) and enables you to get through.
As for forms of attack, as a Wizard you can afford some versatility. It's generally a good idea to pack Orbs - Enervation is stopped by negative energy immunity or simply if your opponent happens to be undead (Necropolitan or Lich, e.g.) in addition to SR and ranged touch. I wouldn't also worry about Spell Resistance all that much; as long as you keep your caster level up there, getting a relevant amount of spell resistance is a lot of work and generally only available through the spell named "Spell Resistance", which gets dispelled among the rest of them. That said, Orbs ignoring SR is a nice bonus.
Force Walls and such are a pretty handy tool - nothing stops targeted attacks like breaking line of effect. Maw of Chaos is quite possibly the best attack in PvP; it's unstoppable damage (other than by being a chaotic outsider) after which it requires a save. If they fail, they'll get damaged again. You should naturally pack means to hit any save lethally; some manners of domination, some manners of death spells and whatever you can scrounge up for Reflex-save should all be around for when the chance comes up to hit someone's weak save.
Mostly though, simple damage along with dispelling is the most reliable way to attack in high-level caster vs. caster combat simply because being immune to everything is so easy. The good news is that you're a Wizard; you can afford to prepare a huge array of different types of offense. Summons and callings are definitely something to keep in mind too; when it comes to opponent being v. hard to affect yourself, Gating in a Great Wyrm Gold or some Abominations can do quite a bit for you, as can just summoning Dispel bots and simple attackers while you negate the opponent's mobility.