Yea, He can be "the next president of the United States", but the probability of that happening (1 out of 300 million if all americans are alike, which they obviously are not) is more than 30 times the probability of you getting hit by lightning twice...talk about cool 'can be' thing. (source : http://www.jewishworldreview.com/0204/glad_u_asked020504.asp)

The benefit is probably you can get a middle class girl to marry you relatively easily. You can probably also get a government job relatively easily--which means 50-100 K depending on your education.But citizenship alone doesn't solve most of the problems otherwise you won't be seeing so many rednecks around with no education or homelesses in the street. It depends on your own caliber.

The loss of getting US citizenship is not obvious, if you don't care about things such as your country, patriotism, getting opportunity to meet your relatives frequently, going to pashupatinath et cetera. Over time, you might miss the safety net of the home and the clan, but these days most of the people have their relatives in the states anyway. You will also not be able to change the world, and perhaps sometimes you may feel guilty that you left a country that is impoverished and probably needs you.

I often laugh at people who become citizen of the states, and then blame Nepalese leaders for this and that. I hope you won't do it. It is like leaving your home and blaming your father for not keeping house clean and becoming prosperous. If you become US citizen, just enjoy life around you, and if you can, go home and help some cause. You owe it to the people back home, but it is upto you. You can always feel you don't owe anyone jackshit, and drink beer and enjoy your life here.