While I personally dislike a lot of the sacred cows (the d20 as a resolution mechanic and Vancian casting being at the top of the list), I don't actually think D&D would be better without them. It would just be a different game, which is why they're sacred cows in the first place.
The question is how to design a game that works with those sacred cows, rather than fighting them. For the d20, I'd like to see large bonuses or mechanics like rerolls or floors to take out some of that randomness. For Vancian casting, I'd also like to see other options, arcane and divine.
I wouldn't like D&D better if it switched to 3d6 or a dice pool system. And I wouldn't like it better if it abandoned Vancian casting in favor of something else. I've got a whole shelf of not-D&D and I don't foresee D&D fighting with them on that basis. It just has to be the best D&D it can be.
Cheers!
Kinak