I don't know much about CSS sprites. If you can get them to work that way, go for it. As for the personality and trade agreements page, I know I initially separated them and then consensus was to put them back together. If we were to add images, we might think about separating the page again. That page lengthwise doesn't need to be even longer. The big reason to add images is to make it consistent with the rest of the pages. That being said, the page is already pretty full.
The big push I had these last few days was to fill in some of the missing rising tide images and to fix the terrain, improvements and resources pages.
A bigger issue is the fact that many of these images have transparent backgrounds while they are white colored, It works fine on PCs but they don't show up at all on mobile platforms. Mobile platforms default to white backgrounds. I also assume this whole site will also change its color scheme soon because of Civ 6 being the main Civ game coming out, and the sites current scheme is for Beyond Earth. It is something to keep in mind.