Galactic Wonders introduced similar to Civilization 5 would be a nice addition, [...] giving a special bonus to the faction controlling this wonder.
Certainly good idea. Right now there are not many buildings which give significant boosts to the empire.
Dead Worlds converted to Minor worlds
One endgame content for sure. If I can terraform my normal planets by 5+ tiles
why can't I get these +5 on any dead planet?
Maybe using some special starbase class which allows the manipulation
of dead worlds.
One addition:
Building structures on one planet and sending them with a huge ship towards
a target planet. This would also include starbases which you could predesign and
just deliver to the point in the map where you want it (of course considering ship range)