Really depends what you’re chasing. If you want overall performance then 256GB is the better choice. It’s quite a bit faster than 128GB in terms of actual physical chip performance. There are diminishing returns in performance once you go above 256GB.
The technology required to travel to another inhabited planet in a different solar system implies so many things. There’s no way we’d ever detect them. They wouldn’t need to even orbit Earth to do whatever they wanted.