Thirteen habitable moons = thirteen tiles. The planetary background artwork would be interesting.
Interesting yes, and also probably realistic. A spacefaring civ would have outposts on moons, on the larger asteroids, maybe even comets in addition to their main colonized planets. Plus a bunch of artificial habitats. But in game terms, I think it just adds more micromanagement. It would take forever to build anything besides early-tier buildings, since you couldn't start with a factory. Each moon would be a separate invasion target too. It would take more time and micro to capture the system, and you're not getting much in return for that effort.
Also, for systems that have only type "0" planets and nothing else, you won't have a more populated, habitable planet to provide influence cover. These single-tile outposts might flip as easily as outlier mining posts do now, so you'd have to build influence starbases to protect them. I'd like a way to reduce the time I spend having to manage starbases, not add more reasons to build them. It's not my favorite part of the game.
If Stardock could figure out a way to make it
fun, and
easy, to add small, single-tile outposts to a system, I'd be for it. Maybe something like clicking on the star to pull up a single window for managing all small outposts in a system, so you wouldn't have to do each one separately. And some kind of single invasion process for all small outposts. Something like that. But I still think influence might be a problem.