I solved the problem. It turns out I hadn't removed the mods after all. I found copies in my \Program Files (x86) directory, and deleted those, forgetting that TS3 resides in the 64-bit directory. I got suspicious when I looked around in the 32-bit directory and it didn't seem like there was a complete installation of the program there. The mods were still in the 64-bit \Program Files directory, and removing them resolved the issue. It looked like a mod-compatibility issue because the symptom (lack of socialization options) was similar to problems I've had in the past, but I was certain I'd removed the mods.
I think I have a workaround for the blank info panel problem, too. Right-clicking on a playable sim to select it causes the info panel to reappear. I've only noticed this problem in new games started after installing ItF, not on older save files.