One thing I would love to see, which would also make playing maps larger than medium more doable for me, is to add tax and production sliders to the colonies screen in the civilization manager. It would also be nice, but by no means necessary, to have totals for population/production/research/morale at the very bottom of each column.

Right now it's rather tedious to have to open and close the domestic screen to change taxes so I can get a certain planet's morale to 100%, or to switch between the colonies screen and the domestic screen to see whether I should focus spending on research or social.