As of right now, you get the tier of NPC tenant depending on what planet you put them on. This limits your places to build a colony if you want the best items and rent. My suggestion is that instead of the location determining the tier of NPC, why not be able to buy different level Colony deeds? The first level could just cost money, but the later levels cost resource bars. So the highest level would cost soloarium. This would make it so you can't get higher levels too early. It forces you to go to higher level planets before you can get higher level people. With this idea in mind, during late game you could build a space station colony that gets you high tier money and merchants, or in fact build your city where you want without losing access to higher tiers.