You do realize that you just pulled a statistic out of your ass? "Not as many ppl wanna be a doctor"? In every damn college in the country hundreds get refused each year to study medecine. What you said is downright false. Our salaries might not be as impressive as the ones in the U.S, but, trust me, they are more than satisfactory for the doctors themselves.
If you really want to sink lower, say that canadian standards in health care are lower than in the U.S again.
Regarding the initial question, logically, a superpower with good, although sometimes questionnable, intent, should theoretically police the world. The problem is that the resources that would be necessary to dish out in order to do so would be downright fiscally impossible. So many countries, ranging from the downright corrupt (think Africa) or with very doubtful democracies (recent example: Belarus) would need cleaning up, but what real advantage would there be to gain?
And what if they don't want to? A lot of countries would react like Iraq, and the last thing the U.S needs is a few dozens Iraqs on their hands. So, unless the whole bunch of real, rich, democracies would care to help, the U.S shouldn't do more than they are doing right now, unless their safety is in danger.
On the other hand, I still think that we could start helping countries that need it without as much as invading them. If they signaled interest, we could cancel their enormous and crushing debt towards us, invest money with protection against ravenous interest rates for them, and send a few employees overseas to shape up the whole government. Even though much of the corrupt governments are very comfortable where they are, I believe a few have signaled enough interest (Mozambique, for example, I think) to warrant help. Then others would probalby follow suit.
