Having a more hands-on approach with battles will in no way detract from the game being a strategy game.
Planetary invasions can still be much more interactive and still be strategic instead of tactical.
Instead of controlling troops or squads like some sort o' RTS, instead be able to determine which improvements, etc., that you'll invade. Dependent upon what you haven't smoked from above. Could be one, two or all.
The defending player can choose which they'd defend, etc.
Such a mechanic will allow for quick choices, thereby not slowing the game down, and provide the player with another layer of control that will immerse them even more within the game world.