Science and Technology: What's the smartest SDG target?

As reported in the Wall Street Journal and TIME.com, expand open international circulation of skilled workers by 5-20% of current skilled migrants, which will return 15 dollars for every dollar spent. Over the period, the benefits could reach almost half a trillion dollars.

The main report proposes a novel idea to promote technology transfer across nations: increased circulation of skilled labor within ‘innovation zones’. Countries that agree to be part of these zones would allow some skilled labor to freely move between them for up to 10 years. 
 
If implemented in the Americas, a 5% increase in skilled migration would mean an extra 136,000 managerial and technical workers migrating. They would earn $15 billion more over the next 25 years.  Moreover, as they would bring with them new ideas and concepts, they will increase productivity in the US and elsewhere by $1.5 billion.  For every dollar spent, this target could do 10-20 dollars worth of good.
 
With the Americas making up one-third of the global economy, and 20% more visas, the potential benefits could go as high as $500 billion for the entire world. That should make the target of higher labor mobility a strong contender for the world’s next set of goals.
 
Another, but less cost-effective target would be for all countries to increase their research and development investments, making all workers more productive. The benefit is about $3 for each dollar spent.
 
You can read all the papers on science and technology here and download the one page PDF here.