How much more money are we going to spend on Afghanistan's infrastructure?

According to the below news article, the U.S. is considering spending millions (on top of millions already spent) to build a solar power plant in Kandahar.

(1) What are your thoughts on this? (2) Isn't it time for us to stop rebuilding the infrastructure of other countries and focus on rebuilding our own? (3) How is this kind of spending benefiting the American people (who, after all, are the ones paying for it)? (4) How is this kind of "investment" even sustainable, given our current debt?

http://www.washingtonpost.com/world/asia_pacific/as-us-withdraws-from-afghanistan-darkness-falls-on-talibans-birthplace/2015/05/08/51ca4348-dd76-11e4-b6d7-b9bc8acf16f7_story.html?tid=HP_more?tid=HP_more