I realized my game (asymmetric 4X in space) has a serious design flaw. So, I'm back to the drawing board and to the initial idea which is focusing more on the tower defence part than on the 4X part. Disregard any prior knowledge you might have about this project, I want to give it a fresh look.
Basic mechanic (do not change unless REALLY important):
Galaxy is made of 300-500 systems/planets (each system is one planet), these are connected by starlanes, you start in the very middle and control like 50-100 planets. Via the edges of the map (from another galaxy) or via transdimensional rifts (or via whatever, it's less important and I can adjust) enter evil aliens that want to kill all life in the galaxy. They do so in a tower defence style by sending waves. They traverse the space (exact rules of movement can be adjusted if you desire, the default rule is they have to take over a planet before they can move to the next one) and aim for your homeworld (the planet at the very center of the galaxy) once it falls it's an instant game over.
Additional mechanic (OK to be changed):
I would like some other, local alien races, to inhabit the galaxy. They would be part an enemy (compete with you for the planets) and part an ally (since you are in the center and they surround you and the evil aliens start at the outskirts they need to move through these local aliens first and therefore local aliens can be treated as a free cannon fodder).
The goal of the game could be to control XXX planets and survive Y waves of evil aliens invasions.
I'm a bit worried about the local aliens, like if it wouldn't be so easy if the evil aliens need to pass through their territory first. Maybe make some rule that the evil aliens can skil/jump over their territory? Hmmm....
Another thought is how about planetary defences? I guess in this sort of game these should be important? Any maybe exert power to neighbour planet as well? Anyway, wild ideas here might be feasible.
I don't have a specific question, post anything you find might be useful (compatible with the basic mechanic part).