See, I've played, and DMed dozens of game sessions, probably even hyndreds of game sessions, at high level. No one was irrelevant. The whole "team" was needed or they would never have beaten the opponents they had.
The only thing extra cool about mages, and cleric types, was they could do a ton of things outside of combat. Fighters can't. Unless you have a player who is excited about his fighter type making his latest suit fo armor, or weapon. Or something similiarly mundane. Which only became cool when the spellcaster used them as their craftsmen for the next magic weapon or armor they wanted to make.
Plus, in 3E, my two experiences with going EPic level, especially beyond 30th level, is that the mage became seriously irrelevant. It seemed everything had immunities and super high resistances out the wazoo. The only solid contribution wizards made was to buff up the party a little bit. Unless they got lucky and cast the one energy type, or one of the handful of other spells, the creature wasn't immune or highly resistant to.
It was the fighters who rocked and rolled in the Epic levels. The wizard became practically obsolete.
I hope your right about the way its going to come together in 4E.