I thought you might be interested in a save that will let you see what the end game is like:

https://www.dropbox.com/s/m6y6pfdzsoz84x4/End%20Game%20Tedium%20Under%201.50.374227.1.GC4Sav?dl=0

Here are the issues I think you should look at:

1. Why haven't I won yet?
2. You should consider combining the results of all mission ships in one screen each turn.
   1. One screen for treasure hunter results (if any)
   2. One screen for research mission results (if any)
   3. One screen for mineral hunter results (if any)
3. Planets that have improved all available cells and that cannot add any more cells should have an option to do something continuously until:
   1. they can add another cell, or
   2. a new improvement becomes available (even if there are no available cells because you may want to destroy an improvement to build the newly available improvement), or
   3. they come back in to stop
4. Shipyards need to have an option to do something continuously until told to stop.

The above suggestions are in addition to the ship stacking and combat suggestions I posted earlier.

I think you will find that playing the game from the above save is no longer enjoyable, it is just a slog to the end.