Yup, I loved both those games. SimEarth in particular would be fantastic for a remake... lots of stuff you can learn about climate change from that game. Maxis did such excellent work building the systems that you could probably work from the original sim logic and build something massive in Unity mostly focusing on the graphics.
Even the spiritual successor Cities Skylines is getting old at this point. There's a few other city-building games that almost nail it but the devs always add in something that makes it too micro-managey like production chains.
Personally I like the production chains in Cities Skylines. I feel they add purpose to the design of the road network and handling of traffic problems. I just wish the AI was a ton better (there are a few mods that help though).