Falling Icicle
Adventurer
Go back to considering Magic Missile to be one round's worth of damage. So, at level 30, one round's worth of damage is about 12.5(25 divided by 2 to account for the chance of missing). 6d6 averages to 21. So a successful crit is nearly two rounds worth of damage. Let's cut it back to one round, on the grounds that sometimes we won't get to apply full damage because we killed the enemy with it. Under that assumption, every critical hit shortens the combat by at least one round. Given that the length of combats is what we're discussing here, that is not insignificant.
So the battle takes 19 rounds instead of 20, a 5% reduction in time. Yes, that is insignificant. And the point remains, even with all these daily powers and the potential for crits, combat at high levels is still taking alot longer than combat at low levels, due to the HP scaling far exceeding damage scaling. Nobody really has managed to dispute that point, and that was the entire matter of discussion. Remember, the 1st level Wizard was doing 33% of a creature's HP in a single attack, but only 9% at level 30. The extra 2 points of damage, on average, from the MS crit, doesn't even come close to restoring that balance. Even if the 30th level Wizard scores several crits, it wouldn't be enough.
I really think that 1/2 level should add to damage, just as it adds to everything else. That simple solution would go a long way toward fixing this problem.