Go for it bro.
the biggest pros are
you can travel anywhere without a problem and lots of headaches .. and you will be treated with some dignity abroad. 
eg. showing US passport  at British AP  is lot different than showing Nepali passport. the haedaches of getting visas to go anywhere  is always there if you have nepali PP and green card. 
You can choose to go back to nepal and live there for as long as you want but end of the day you can come back to US if things dont work out there. if you are traveller and get caught up in trouble or disaster, anywhere in the world perhaps you and your family will be rescued/helped if you have that blue passport. If you have nepali passport you aint gonna get shit. 

So, give up that green and get the blue my friend , you will like it. as long as you wish well for the country and have it in heart thats you will be fine.i was in same dilemma 3 years back and now i am so glad i did it. everytime i go to nepal i love nepal more but at the same time i do feel proud to be an american citizen. 

btw you can also drop the idea that nepal will get better one day.. in last 22 years (since 1990) it has gone worse from bad.