When Robert Downey Jr. played the alcoholic hero Tony Stark/Iron Man, it changed who could play a superhero and how a superhero could be played in a big, comic book movie. Downey brought eccentricity to superhero movies. He didn't play a stoic or a bad-ass or a cocky motherfucker (or more accurately, just a cocky motherfucker), but a person who takes on not a role or persona, but a larger cloak of responsibility. This is, of course, what super hero comics are to comics readers but not the general public: Humane stories dipped in superhero stuff.
Nicolas Cage, certainly an eccentric actor, but also a comic book fan and comic creator himself, would be able to put the stoner perfect world of 60s Ditko into the contemporary world, without the ironic tinge that most would undoubtedly employ. Cage understands his place in the world of Hollywood better than most. He plays serious sad guys in movies like Weatherman with the same sincerity that he presents in movies like Con Air, where he plays a weird not-so-tough not-so-sexy tough ass sexy dude, and even in weird stuff like The Wickerman. Instead of becoming these characters, he becomes who those characters see themselves as, like when ten year old boys draw themselves with sunglasses and chain wallets. He's painfully sincere. Always. This understanding of the character he's becoming has been what's allowed him to present them in a way most people would over look, exaggerations that define his roles.
Ditko-Era Dr. Strange is all about weird eccentricities like these; garrulous spells and exaggerated hand motions. Cage's ability to be completely aware of who and what he is while still putting on a "show" would be perfect for Dr. Strange. His serious but goofy demeanor would award Dr. Strange the respect he deserves--other actors would try to create an aura of mysticism that would be too mannered and thought-out. Strange is Sorcerer Supereme, whoever acted these incantations out would have to not only believe them, but would have to be able to say them as naturally as he walks. Cage could do this.