I do so worry about building up units with XP only to see them become obsolete and overshadowed and too expensive to sensibly update. And then I want to update them anyway. But playing the long games I will have a barracks everywhere almost and just a couple of monasteries. Organized religion is almost a whole game thing for me because I am playing deep, and it takes a long time to build factories. If I were playing a little Pangea map and 7 civs it would all be different I am sure.
I have the annoying habit of having annoying habits. For example, I don't like to chop for a unit I might lose, it seems to make sense to me to chop infrastructure I won't lose so that's what I will do, sometimes infrastructure I don't have to have. I endlessly post sentries and scouts for attacks that never come, obsessively leave forests on plains so that I can build lumbermills so that I will maybe not have to build some health-related building. I will leave squares empty for ages just in the hope that a forest will grow that I can chop. My worst habit is to build blocking settlers for those odd squares not in my cultural radius, to prevent encroachment, which I have to do because I play limited war rules. These habits are rabbit holes that are almost like black holes. Just can't get away from them. So, I end up using settlers as scouts on distant continents in the latter game. It is a mental condition of some sort.
The fact that I have come back to Civ IV after all these years is, I suspect, a clue the white coats are coming.