You know there wasn't always a 15x mega rich limit even. Terraformer draws went on long after that limit was imposed. Some of the people that were high level early on have some pretty ridiculous planet collections. That whole strategy got slowly nerfed though. I leave enemy icy planets alone just to see if they want to use a mass-surface ice melter on them before I invade someday. I turn in down to 4000 as often as possible just to get rescued prisoners but I imagine artifacts will be pretty much useless once I have enough decks for everything. Most consumables pile up faster than you can use them unless they can be used on an NPC blitz, which is pretty much flat out the fastest/best way to level now.

Maybe if you could scrap artifacts for 10-20% AP it would be worth it for more people. WTF else can I do with subspace seekers and half of everything else?

Depends on the value you put in them; depends on your strategy. Everyone has their own. Someone might even have a complete disinterests on the artifacts you consider to be most valuable. Even the issue of taking full advantage of artifacts still depends on the players judgment. Right now, I don't see any real problem in the artifacts system.

Depends on your schedule or when you don't like what you're collecting anymore.

Rescued prisoners will never be useless. Even once you have enough decks you can spend those points on engineers, helmsmen or tac officers. Thats still increasing your energy, attack or defense. And don't forget brackets and x charge cells. Ten hull or 5 shields doesn't seem like much even long before those levels, but getting a steady supply of them will significantly increase your hull and shields over the duration, and once you've researched all the tech trees and have the mods installed, it's the ONLY way to increase hull and shields.