Yeah, passion is extremely important. It's interesting to see how medical schools (or at least UT Houston) is going well out of its way to promote humanities in medicine. Unfortunately, I know quite a few that are in it only for the money. Hell, I'm pressured by family most of the time with the notion that I MUST specialize rather than be a general physician because otherwise I will have less cash to roll around in. e_e

As for grad school, judging by my brief foray into looking at them/trying to find the right PI and research group, it is so hard if you don't have something very specific in mind. And since you love nearly ALL THE THINGS...yeah, pain. XD I'll let you know if I see anything crazy awesome.