ROI is always a hard thing to explain when it comes to space exploration; remember, the idea behind the base is that it will be a stepping stone to Mars (teaching us about the technology we might need for a manned Mars mission). The good news from that point of view is that it doesn't look like NASA is getting extra money for the project so much as channeling money that was going elsewhere into it as other projects reach the end of their lives (i.e. the space shuttle).