WTF? It's fantasy with wizards, elves and dragons, and you're talking about suspension of disbelief? If it's an Asimov or AC Clarke adaptation maybe we can start talking about believability, but a high fantasy like this one? Anything goes, except perhaps when it comes to absolute immortality. Apparently "immortal" characters or monsters tend to have some sort of weakness that allow them to get killed by a determined hero or villain.
Suspension of disbelief is a challenge and probably more important to maintain in a fantasy than general fiction. A story must maintain internal consistency with it's own tone and rules. If you tell me that a dragon can fly and breath fire, well then I'll believe you, say Elves exist and can make pineapple smoothies by snapping their fingers, and as long as you don't have one of your Elves die of starvation because he didn't remember about the smoothie trick, it will work. The magic wasn't a problem in the Hobbit, it was the tone. The movie constantly shifted between extreme slapstick humor, to somber memorials of beauty forever lost, back to grossout gags, sudden videogame action, and into gritty graphic violence. You can't do that and expect to keep the audience. You have to pick something and stick with it, otherwise we don't know what movie we are watching.