Have you tried following a tutorial on those genres? Generally what happens is that mid-tutorials you end up inspired on different features.
A game doesn't need to re-invent the wheel to be good, sometimes it's just a small change.
That said, an Idea I had a while ago was "Ants RTS". A game where you have to choose your ant colony and conquer the backyard vs other colonies. Warrior Ants, Archer Ants, Monk Ants, etc.
It is a complex idea though...