Replying to Study abroad or plant trees?

I got accepted into a program where I will learn about economic development while working with an NGO in  the middle of nowhere in Bolivia for three months.  The program will pay for 70% of my costs, excluding tuition.

I am also thinking about planting trees in BC and going down there on my own (I really want to get my Spanish skills up).

If I do the international service learning program I get to spend a month skiing/biking in Whistler before I go, which would be awesome.  Have any of you done a program like this, where you spend your summer working with an NGO in a third world country?  How was it?