Maybe the suggestion has already been made, but wouldn't it be nice to be able to change
the planet description in the planet window? My games can takes weeks to complete, because I don't have much time to play and for me it would be helpful and fun to be able to add text to the description to remember game events. You could create some more story for yourself, by for instance adding text like 'This planet was taken from the Torians after they back stabbed our empire, by cancelling all our trade routes and declaring war'. Or something like 'Remember that you wanted to make a high-pop planet of this one.'