I'm strongly considering it. I unzipped my old copy of civ1 and took a bunch yesterday just fooling around. I don't know that I'd actually use such a mod, but I just think it'd be fun to do

The graphics for units, techs, and improvements won't be hard to get since those are all in the civilopedia. And wonders can probably be cheated into a city and copied from the view. You've already got all the terrain & such, although I'd like to see how it looks unrotated, but that's not exceedingly hard to get either.
The real bear is the leaders. You see, I had this idea to copy the leaderhead images as well and even have them "animated" since the civ1 heads do show expressions and blink their eyes and such, but capturing all the frames is the problem

The advisors behind the leaders in negotions also show expressions, unlike when they are advising you, so I'd want to get as many of those expressions as I can to use in civ3. I got a bunch of shots of Shaka in a test but I have to figure out exactly how many frames there are and try and capture them all. That's the one area where not knowing the graphic file format hurts

Even my trusty copy of Rome on 640K per day doesn't say how to get at them easily.