Something WW had more of than a lot of the other main console Zelda games, I find, is expressiveness and humor, the "charm or magic" of the game as many have already pointed out. The art style contributed a lot to both. I think WW would lose more than it would gain with a different art style.
WW Link was one of the, if not possibly THE most expressive Link we've seen. OoT and MM Link had no real personality, TP Link did, but it was mostly bland, SS Link was better but still not quite there for me. WW Link reacted to everything, from his sleepy surprised face at the beginning all the way to his sad desperation at the King's sacrifice at the end, and everywhere in between (annoyance at the Hero's Clothes, embarrassment from the Fairy Queen, the entire cannon to the Fortress sequence, etc). The art style was simple, crisp, exaggerated, vibrant, it amplified his expressions in a way that would have been lost with a more realistic style.
The same applies to the humorous elements of the game, which included everything from story (see again cannon sequence) to enemy design (ever poke a Moblin's backside?) to even minor things like his face when he's lifting something heavy (seriously, pick up the giant pig and tell me TP Link could pull off that face). Cartoon exaggeration is what makes things like that possible.
Without the toon graphics, WW would just feel like a less epic OoT to me, honestly. WW is not the most epic storyline, you aren't faced with imminent destruction, there is no air of danger or immediacy, you aren't a "Chosen Hero", you're just a kid who wants to get his sister back, then find yourself unable to turn your back on the greater good. But what WW lacks in epic it makes up for in charm. It just would not be the same game without that charm.