I bought the original when it came out and, together with Master of Orion, it ate so much of my life that it added a year to my time at university. Since then I've bought every new Civ as it came out and maybe played through two or three games before abandoning it. None of them capture the original, but rather just add more and different crap to micromanage. They're just not fun. The big exception is Alpha Centauri,…
Since owning lots of cities essentially comes at relatively little cost in the older Civ games, towards the end the AI will have spammed cities in just about every nook and cranny. (The addition of sea bases in SMAC seems like an interesting addition at first but accentuates this problem.) In SMAC the relationships with some of the AI leaders also tend towards more or less perpetual war which, with the high number of cities, I find frustrating since striking down or conquering a chronically belligerent neighbour requires capturing (or razing) a ridiculous number of individually insignificant cities.
Shifting the maintenance costs of units from individual cities to gold paid from the treasury also reduces micromanagement of those unit costs. Having cities defend themselves at some level without having units stationed also reduces the need to micromanage their defences in some cases.
I haven't played the first Civ that much but I played a lot of Civ II, and I think it suffered from some of those issues as well.
It's true that some of the changes in later Civs do also add further micromanagement. The archaeologists added in Civilization V: Brave New World require going all over the world (and generally hand-holding them), and the entire mechanic seems like a bit of an odd but more or less compulsory detour in the game. And optimizing the great works stuff in general quickly turns into micromanagement. Dealing with e.g. city-states and their quests also introduces some of it, although they also add another (potentially interesting) strategical conduit to the game.
With that said, I still find SMAC to be one of the best games in the series, and there will always be a place in my heart for Civ II.