"In this type of game, it's not that the task is not fun. At first it is fun, when you have only a handful of thing to manage. But as your empire grows the fun tend to go down, and it become repetitive. I have the same feeling when I play the likes of civilization, or even the total war serie."
The solution is to have something more automatic
"What exactly is the point of having detailed decisions for things like build orders if the user doesn't actually make those decisions?"
How an emperor rules ?
By giving order, and doing micromanagement every times it is needed.
So I think a very enjoyable game would be one where you start with a small number of planets, taking every decision, then as the number of planets grow you are able to make "plans", for example if you have ten planets with almost the same set of ressource, you would be able to replicate all the buildings and structures you have build on the first planet in one click.
You would also be able to give order according to some possible events, such as "if there is no more ore on the planet, reconvert it into post industrial planet" or "begin colonisation as soon as the ship arrive if the planet satisfy some requirements"
Each orders or plans would be designed by the player who would also have all the micromanagement power he wants.