In the Develoment screen, one of the green sliders is "Development". What does it do exactly? When I add to it, it doesn't seem to add to any of the totals over on the right. And I build improvements without it, but does it speed those up?
It speeds up building improvements. If you watch carefully, you will see the number of turns it takes to build something reduce as you add points to this slider.
PS you may have to add more than a few point to see a change.